Archive of Our Own

“Whoa,” Izuku said, setting his bags down on the bed in the middle of his new bedroom. His plane had gotten in late, so the sun setting beyond the sliding glass doors burned bright and red, dipping down to soak into the horizon. 

Just past the glass, an expanse of soft white sand gave way to the ocean. Despite the late hour, a few hundred people—locals, it looked like—covered the beach. Judging from the cabanas, torches, coolers, and a blazing bonfire, they were throwing quite the party. 

Izuku’s new manager and the house-representative, Sasaki, followed Izuku’s gaze. 

Sasaki made a dismissive sound in the back of his throat, doing nothing to hide his contempt. “Ignore that. You’ll do well to not get distracted by parties anymore.” 

“But…” 

Izuku wasn’t much of a partier, to be honest. He knew lots of competitive surfers were, but for him, he surfed for the love of the sport—not for the lifestyle that often came with it. Yet there was something about the raucous party outside the beachfront house that called to him. Or, no... It wasn’t really a party, he realized.

The joy on the people’s faces was so sincere. The way they danced, too, with practiced bare feet kicking up graceful arcs of sand, stalled Izuku’s  breath. He suddenly yearned to join them. He wanted to dance, too. 

“What are they celebrating?” Izuku asked, because that was the right word. Not a party, a celebration.

Sasaki sighed, stepping forward to close the curtains. “The locals are convinced that a mermaid has moved into the reef. Something about new coral structures. It sounds like wishful-thinking to me.”

“A mermaid…?” Izuku whispered, still staring at the spot in the closed curtains where the bonfire had blazed. Izuku had always wanted to meet a mermaid… Once found in nearly every body of water, mermaids had grown increasingly rare since the industrial revolution. Their numbers were now bouncing back, but mainly through their own resourcefulness and adaptability rather than through human’s efforts. Mermaids were often incredibly elusive, however, so a true count of their population was practically impossible, though estimations could be made by studying the surrounding habitat. Izuku wondered if—

“Quit rambling, Midoriya,” Sasaki snapped. 

Izuku jumped, slapping a hand over his mouth. He hadn’t meant to start muttering like that…

Sasaki continued, “You’re not here to daydream about mermaids. You’re here to win competitions. Training starts at 0600 tomorrow. I need you rested, clear-headed, and ready to work hard. UA Waves took a risk in sponsoring you and while I respect their decision, I will not hesitate to kick you out of the Alliance House if I think you are not committed. Do you understand?” 

Izuku ducked his head, cheeks burning. 

“Yes sir,” he agreed. 

—

Five Years Later

—

Sunset was the best time on the water. 

It was when the air lost its oppressive heat of the day, and the turquoise sea suddenly sparkled golden. It was when the waves curled into perfect frames, catching the sun within garlands of seafoam and salt. 

And Izuku felt free at sunset. His lessons were usually wrapped up for the day, and only the most dedicated of surfers lingered with him, hoping to catch one more wave. While he floated atop an ocean of liquid gold and watched the first stars of the night wink into existence overhead, his worries just… disappeared. There was no room in the blissful quiet to think about rent, to think about the future, to think about the past. 

For a handful of minutes everyday, Izuku could just… be. 

The day Izuku received the first gift was the same as any other. 

His last surf lesson of the day had concluded a little later than usual, so Izuku had only just paddled back out when the sky began to turn orange. 

He sat up from his paddle out and sighed, pushing salt-curled hair back from his forehead and idly wondering if he should cut his hair like his mother kept hinting at. After a moment of thought, Izuku unzipped his wetsuit halfway and tied the arms around his waist. He wanted to enjoy the last of the sunlight.

The sun didn’t disappoint, warming him even as drops of ocean slipped from his collarbones to slide down his chest and stomach. 

“Damn,” Izuku murmured, relaxing onto his board. All the hours he spent working, all the ways he bent over backward just to justify the time he spent in the water… they were all so worth it. Just to be able to sit here, at the meeting point of sky and ocean, watching the sun melt into the sea.

There was nowhere else Izuku would rather be than on or in the water, and there never had been.

The ocean undulated over him, swelling in a long, enormous breath of power. Izuku settled his breathing in time with the waves. He couldn’t match it perfectly (the ocean’s breath was too large for that) but he could still ease his way into its rhythm. 

A promising wave began to build in the distance, but a strange current under his feet snapped Izuku’s attention away a moment later. It felt like the swish of rushing water as a large fish swam by. 

He jerked his head down, alarmed, and caught the edge of something bright orange as it left his vision. He tilted his head and raised himself on his board, trying to peer down at the castles of towering reefs dozens of meters below him. From this far away, they just looked like dark blobs. Nothing else stood out. 

Odd, Izuku thought, settling back down. It must’ve been a reflection of the sun. A moment later, the currents under his board began to crest with urgency. 

“Oh shoot,” Izuku cursed, circling his legs to turn himself around. He paddled hard and caught the wave just as it built into its highest arc. Izuku leapt to his feet, balanced and steady. The wave carried him to shore, indulging Izuku as he swept sideways, and darted back, prolonging his ride a few seconds longer each time. 

By the time he finally reached the shore, he had forgotten all about the little flash of orange he’d seen. Or he would have, had a burning ember of red not caught his eye. 

Izuku stopped and first looked down into the sand to chase the fiery pigment. This beach wasn’t that great for beach combing, but he’d found a few nice shells before. The glimmer of color didn’t reveal itself, however, until Izuku shifted positions to move his surfboard out of the way. Then he spotted it. 

For a moment, he stared dumbly at the gently swinging trinket hanging from the end of his board. Then he reached out with one hand to cradle it closer. It was… a woven bracelet, knotted expertly around Izuku’s surfboard leash. The bracelet held a single jewel within a net of fine rope—a large piece of red seaglass.

Quickly, Izuku unknotted the bracelet from his board.

The sea glass was gorgeous. As a child, Izuku had helped his mom collect sea glass whenever they visited the beach. She had been choosy about the pieces she selected, only taking home the ones with perfectly smooth edges. The others she had tossed back into the ocean, declaring that they “weren’t ready.” 

This one was absolutely “ready”, perfectly smooth oval from every angle with no chipped edges. It was also large, nearly the size of his thumbnail. The color was a gorgeous, uncommon red that seemed to shine with an inner light despite the even frosting of the glass. Izuku held it up to the fading sunlight and marveled at the glimpses of orange and blazing yellow created by tiny imperfections inside. The bracelet itself was also crafted beautifully. Every knot was tiny but sturdy, and when he impulsively slipped the bracelet over his wrist, it fit perfectly. 

“Wow…” Izuku breathed. 

Izuku knew that if his mother had found this piece of sea glass, it would have been the prize of her collection. For a moment, Izuku considered giving it to her, bracelet and all. Then something all-encompassing and possessive swept up from his stomach to his throat, and Izuku clenched his fist around the tiny gem protectively. 

No, he thought, This is mine. 

—

The next morning, Izuku stood waist-deep in the shallows of the ocean. He held his own surfboard at his side and had his hand on a second one, steadying both it and the child it carried with ease. Half of his mind was on the surf lesson he was currently giving, and the other half was caught—again—by the woven bracelet on his wrist. 

First off, he kept admiring it. The bracelet may have genuinely been one of the most beautiful things he’d ever owned. 

Secondly, however, his mind kept turning over the mystery of the bracelet. The more he thought about it, the more confused he’d become as to how he’d gotten it. Bracelets usually didn’t end up tied to people’s surfboards, after all. He supposed that it could have been caught by a current and tangled against his board but…

“How about this one?” Izuku’s student on the board, Kouta, pulled his attention back from the red gem to the gentle waves building around them. Kouta was sitting eagerly on his knees, eyeing the shore like it was a challenge he could win. Izuku immediately smiled and refocused, appreciating his student’s enthusiasm.

“Oh definitely!” Izuku agreed, feeling the wave build around them. “Okay just like we practiced on land, alright? Paddle hard! Paddle, paddle paddle…!” 

Izuku stepped into the wave as he spoke and pushed Kouta’s board forward, assisting his paddling efforts so that the child easily caught the bubbling mass of the broken wave. Kouta stood up just like they’d practiced, going from his stomach to his knees to his feet. He landed a little off-center on his pop-up though, and toppled sideways into the wave. 

“So close!” Izuku called when Kouta splashed to the surface, spluttering indignantly. He jogged forward to fetch the boy and held his board steady as Kouta clambered back on.

“You just gotta remember to plant your feet evenly. Remember how we practiced on the shore? Feet in the middle of the board, knees bent!”

“Knees bent,” Kouta repeated, his mullish expression morphing into determination.

Izuku towed them back out to where the waves were at the ideal level for a six year old. Then they went again, and again. By the end of his hour Kouta was standing with every wave, shouting to his parents who were enthusiastically taking pictures from the shore. 

“One last wave little guy, are you ready?” 

“No!” Kouta protested, throwing a betrayed look at Izuku over his shoulder. “Can’t I have…” He hesitated and looked down to count his fingers. “Five more?” He asked, eyes wide and pleading.  

Izuku’s resolve crumbled like a sandcastle to the tides. He’d always had a weak spot for kids... It was probably why he got assigned most of the shifts with the little ones, actually. 

Still, he glanced behind himself, casting a calculating eye at the slowly descending sun. Five more waves would mean that he definitely wouldn’t have enough time to surf himself before the sun set.

Ah, well. There would be other sunsets to surf. 

Kouta’s grin when Izuku agreed made it worth it, anyway. 

— 

Half an hour later, Izuku gently deflected Kouta’s whining protest for just one more, please, and began towing them both to shore. As he turned to watch a wave approach behind them, though, something caught his eye. 

Izuku had neglected his surfboard most of the afternoon. It was really only there in case he needed to do a rescue or if he had a more experienced surfer he wanted to take further out. 

So Izuku’s mind went blank, a little, as he tried to understand where the small conch shell sitting in the middle of his board had come from. Eyebrows furrowing together, Izuku reached to carefully lift the shell from its perch. 

Is it alive? He wondered. He didn’t recognize this species of conch at all, but he also wasn’t an expert… When Izuku picked it up though, the shell was decidedly hollow. Not only that, but it appeared to be… polished. Cleaned. The inside of the shell shone a smooth, burned orange and the rugged edges of the outer shell looked sanded down.

Izuku opened his mouth to ask Kouta if he knew anything about the shell, but stopped himself at the last second. He… didn’t want anyone else to see it. It was too beautiful, too weird, too…

It’s mine, Izuku thought, tucking the shell away into the open space of his wetsuit, which was once again tied around his waist. 

That night, after he’d showered and cleaned up, Izuku placed the conch on his bedside table. He stared at it, as he laid down to sleep, measuring its shape with his eyes and studying the way his lamp reflected across its surface. 

Finally, when the contours of the shell had imprinted themselves onto his brain, he reached out and pulled the shell closer, cradling it to chest. Only then could he finally bear to turn the lights off.  

—

“There you are!”

“Hey, Midoriya! Just in time!” 

“Hi guys. Sorry if I made you wa-ait,” Izuku greeted, interrupting himself to yawn. 

“You’re not late,” Kirishima assured, “Uraraka just got here too!” 

“Yep!” 

It was a little past four in the morning, and despite sleeping a full eight hours the night before, Izuku was exhausted. He’d slept deeply, but his dreams had felt endless. He’d also woken up with his face pressed up against a fucking conch shell, so that probably hadn’t helped.

Izuku was hoping that Uraraka and Kirishima wouldn’t notice the deeply-grooved indents on his cheek and jaw. Maybe he could get away with claiming he’d fallen asleep on his laptop. They’d believe that; though then they would also probably assume that he’d fallen asleep researching mermaids again…

Ah well. Better than them knowing he’d been drooling all over a conch. 

Speaking of his fishing buddies, the pair seemed incredibly chipper as they got ready, throwing various supplies into Kirishima’s small dory boat. 

Izuku went to join them, reaching for his spare wetsuit, when movement in the water suddenly caught his eye. 

Underneath them, the ocean rippled with the movement of the dock, sending bolts of silver lamplight reflections billowing out from the inky blackness of the ocean in ever-expanding rings. The ocean was as dark as death this early in the morning, but for a moment, Izuku could have sworn…

He shook his head. I must still be dreaming a little bit. 

“Midoriya, toss me that bait.” 

Grateful for the task, Izuku immediately complied with Kirishima’s order before throwing his own things into the boat and tugging on his wetsuit.

“You’re looking tired, man,” Kirishima observed, raising an eyebrow.

“Yeah,” Izuku agreed, scrubbing a hand up and down his face before hopping into the boat. “M’honestly not even sure how I got out of bed. Muscle memory, I guess.” 

“You working too many shifts?” Uraraka asked. She’d won the fight with her own wetsuit, and slid into the seat next to Izuku. 

“Nah,” Izuku denied, though he definitely was. “Just… had some weird dreams last night s’all.” 

“Weird dreams?” Uraraka prompted. 

Izuku shrugged. They hadn’t been bad, but they’d been strangely vivid. At one point, Izuku had been surfing, but then he’d been under the water, watching himself surf, which was eerie. At another point, Izuku dreamt that his skin was too small for him. He recalled itching across his arms and torso and twisting, as if he could simply slip out of his skin if he tried hard enough. 

At the memory, Izuku unconsciously brought his hands back to his wrists and itched the soft skin there. It felt good, so he dragged his nails up and down his arms, moving his bracelet out of the way.

The most intense dream though, had been about bubbles. In it, Izuku had been standing on the ocean floor, deep underwater. Bubbles rushed up from the sand below him, and at first, they were just enough to keep him from drowning. For what had felt like hours though, he’d felt as if he was on the brink of suffocation. Until, finally, something had shifted, and he’d been able to breathe. 

“I don’t think I could really describe them,” Izuku finally hedged, “they were just weird.” 

“Well I had a dream that I caught a huge lobster.” Uraraka grinned. 

“Ooh, that’s a good omen!” Kirishima said. Izuku made a sound of agreement. 

“It’s gonna come true,” Ochako announced as Kirishima started up the motor. “There’s a huge lobster waiting for me this morning, I know it!”

“You mean a huge lobster… but within the legal limits, of course,” Kirishima said. 

“Well, of course.”

Izuku allowed Kirishima’s and Uraraka’s quiet banter to wash away the last of his discomfort, and settled into the ride, enjoying the smell of ocean in his nose and the gentle spray against his cheeks. 

The world grew darker as they pulled away from the harbor and the three of them naturally grew quieter in return, dropping their voices down as they cut across the surface of the star-speckled ocean. 

They motored over to a beach a few miles away from the harbor. The beach itself wasn’t very popular with tourists on account of the rocky shore and steep, looming cliffs, but the area was excellent for spear and lobster fishing. 

Kirishima anchored the boat a hundred meters away from where black waves rumbled like a purr against the cliffs. Izuku checked the last of his gear. The waters were colder in the early morning, so he was wearing his wetsuit properly for once—zipped all the way up to his throat. Other than that, he had on his diving watch, flippers, thick gloves, and a headlamp. He had a bag for holding his catch wrapped around his wrist. 

“Everything working?” Kirishima asked, his voice still hushed. Without the roar of the engine under them, they’d fallen even quieter. 

“Yep,” Izuku confirmed, flashing his powerful headlamp on and off to make sure. 

“I’m good too,” Uraraka agreed, pouring a bit of anti-fog solution into her mask. 

“Okay, let’s head out.” 

Without another word, Izuku tumbled backwards into the water. The cold shocked him to his core, chasing any remaining sleepiness from his brain. 

Without bothering to take a breath, he immediately dove down, kicking hard with his flippers and only leveling out when his headlamp cast light across the reef below him. An eel darted out of his sight and a school of smaller fish followed in its wake. 

Izuku smiled around his mouthpiece. 

Despite the contents of his dreams last night, Izuku felt himself fall immediately calmer within the cold embrace of the water. The ocean was home, and being in it now made the anxiety and fear of his dreams last night seem ridiculous. 

Izuku spotted Uraraka and Kirishima’s beams of light heading closer to the cliff, but he decided to swim down closer to the reef for a minute. 

Izuku liked to go lobster hunting with Kirishima and Uraraka every few weeks, but he usually stuck pretty close to his friends, a little too weary of the dark water to risk venturing out on his own. This morning though, he found himself feeling completely at ease within his small bubble of light.

He followed an imaginary spiral staircase all the way down to the ocean floor, slipping between the towering reef structures as he did so. 

Mermaids really are amazing, he thought, casting his headlamp up and down the reef’s face. Branching coral caught Izuku’s lamp and cast shadows like spiderwebs, and anemone swayed lazily in the ocean’s currents, hiding smaller diurnal fish in their embrace. The reef was easily the height of a two-story building, staggeringly large and complex.

Izuku could see where bits of human debris—an old tire there, a piece of rebar here—had been delicately woven into its overall structure, then propagated with all manner of polyps and seaweed until it was covered in life. The overall effect was something like a castle; Or perhaps an incredibly dense city, complete with living skyscrapers. 

As far as he knew, this reef hadn’t even existed a few years ago. But that was what mermaids did. They came to a coastline and they built new reefs up into sprawling, towering structures like this one. Then they built their homes inside them, often carving complex networks of tunnels and dens into all throughout a reef’s insides.

The large reefs provided more space for new coral and plant life, which fed more fish, which attracted more predators… mermaids basically expanded any ecosystem they came into, tenfold. 

Izuku had also read that beaches with an active mermaid presence had less trash, more balanced PH levels, healthier fish, and even clearer waters. 

Izuku’s eyes cast down to the bottom of the reef. A dark enclave, half hidden behind a copse of seaweed, caught his eye. It looked like any other depression in the rock, yet Izuku was suddenly certain that he was looking at one of the entrances to the mermaid’s den. 

In the same moment, he felt a pair of eyes, heavy and alien, settle across his shoulders. 

The mermaid is here. 

Izuku jerked his hand up and snapped off his headlamp. 

The sudden darkness was staggering. The ocean pressed against him on all sides in the same way as the fear pressed in on him, seeping into the cracks of his consciousness and quickening his heart. He struggled not to panic.

But he knew instinctively that he’d done the right thing, because the mermaid was definitely nearby right now. Izuku didn’t know how he knew, but his every instinct sang of it. The mermaid of Musutafu, who was so reclusive that not one human in over five years had caught even a glimpse of it, was hidden somewhere in the darkness.

And if the mermaid had worked so hard to stay hidden, the last thing Izuku wanted to do was invade its privacy.

A gentle current of displaced water pressed against Izuku’s shoulder. If he had been breathing, he would have stopped. 

It’s close…

As if to confirm, a low, melodic crooning filled Izuku’s ears. Izuku had heard both whale song and dolphin song before, of course, but this was different. Soft, ariose, and human, the song brushed across his shoulders and caressed his cheeks. Izuku hummed back softly.

Somewhere in the back of his mind, he realized that it had been quite a while since he took a breath. The thought was dismissed quickly as unimportant. 

The currents pulled Izuku this way and that, and he got the sense that the mermaid was… circling him. He squinted through the darkness, longing to catch the shine of a scale, the glint of an eye, anything. The moon had set hours ago though, and the light of the distant stars wasn’t enough to see by. The mermaid could be right in front of his face and he wouldn’t…

Something touched his hand. Five fingers, a strong grip. Izuku fell as still as possible. The hand toyed with the edge of his thick glove, found the zipper, and pulled it off in one movement.

The mermaid’s song reached a higher pitch, crooning as its webbed hand wrapped around Izuku’s fingers. Izuku’s eyes filled with tears. He could feel them. The mermaid’s hand was soft, the pads of their fingers pressing into Izuku’s. Izuku felt something pleasant and bubble-like erupt from where their skin met. 

What could have only been a tail wrapped loosely around Izuku’s ankle and drew him closer. A warm cheek pressed into his throat and another hand pressed against his chest. Something soft like hair tickled his lips. The song reached a crescendo—a sort of happy purr—and Izuku was helpless to do anything but bring his unattached hand up around to press into the mermaid’s back, where their scales met their skin.

The mermaid was so warm. They shuffled closer, and Izuku felt the crest of a nose against his throat, then the press of lips. 

Izuku felt a rush of—of something fill his veins. Of selfishness, maybe. Of desire, definitely, and of possessiveness. He pulled the mermaid in closer. He wanted to… 

Light flashed across Izuku’s eyes. He flinched backwards, blinded. The body against his own disappeared as if it had never existed. 

No! 

Izuku reached out desperately but the rush of current told him what he already knew; The mermaid was gone. 

The light drew closer. 

Izuku turned to squint against it. He felt… dazed. A little slow. 

Had that really just happened? 

The light turned into Uraraka. She gestured something frantic-looking, but Izuku couldn’t parse it at all. He was stuck on the feeling of bubbles and liquid gold still embracing his skin where the mermaid had touched him, making the rest of his arm feel tingly and soft. 

Had that really just happened? There was no way… right? 

Finally, Uraraka grabbed him around his elbow and hauled him upward, bubbles exploding from her mouth as if she were yelling something. 

They broke the surface and Uraraka immediately grabbed Izuku’s face, ripping his mask and mouthpiece off as if they had offended her. 

Above them, the sun was a whisper on the horizon, lightening the sky into a dark blue. 

“What the fuck, Izuku?!” Uraraka hissed, slapping his cheeks. “Breathe!” 

Izuku did, sucking in a small breath of air, then gasping for it. He coughed up a startling amount of water, his eyes watering. 

Uraraka spoke his thoughts aloud for him, demanding: “How long were you fucking under there, dude?!” 

Izuku thought about it as he coughed, his lips brushing the salted surface of the water. 

How long has it been since we got into the water? he wondered.

But that… didn’t make any sense. Izuku shook his head, finally regaining a little of his breath. “Not long,” he lied. “I was just…” 

Uraraka sighed. “Listening to the mermaid song, huh?” She guessed. “Was that your first time hearing it?” 

Izuku looked up, squinting at her through the salt dripping from his lashes. “You’ve… heard them before?” 

“Once or twice,” Uraraka shrugged. “Never this close though, so I don’t blame you for getting sucked in. S’why I went looking for you actually, it can make you a little…” She pointed at her skull and made a circling gesture. “Well, no harm no foul, though! I’m sure the mermaid didn’t mean to stun you! And now that you’re ready for it, the song shouldn’t mess with you so much. Are you feeling okay enough to keep going?” 

“Keep going…?” Izuku asked. Wait, what was Uraraka doing here again? 

She frowned. “Lobster hunting, Izuku. Actually no, you’re not good to keep going. We should head back to the boat, c’mon.” 

“No!” Izuku protested, pulling away when she tried to grab him again. His mind had latched onto what she said—lobster hunting—with a clear intensity, shaking away the last of Izuku’s confusion. Or perhaps, merely supplementing it with something new. 

A goal. 

“I’m good,” Izuku insisted. “Super good. And we still have another hour or so before daybreak, right? Let’s go get a few lobsters.” 

Uraraka hesitated for another moment, but then smiled, never one to be bogged down with doubt for long. “Well if you’re sure! And you mean a few more for me!” She held up her bag, which, sure enough, was squirming quite bit. “You’re gonna have to hurry to catch up, Izuku! Come on!” 

“You’re on!” Izuku agreed, putting his mask back on. He followed her back to the cliffs, watching carefully as she went up for a breath every thirty seconds or so and carefully mimicking her. 

When they reached the cliffs, Izuku drifted away a bit, using his lamp to find a promising crack in the rocks.

Izuku had never been the best at lobster hunting. You needed to be quick and had to grip them tightly even when they were doing their best to pinch your face off. He usually managed to catch one or maybe two during his outings with Kirishima and Uraraka, but that was enough to make his mom and Yagi happy, so he’d never really worried about it. 

This morning, though, Izuku was ruthless. His hand whipped down inside the crevices in the rock, ignoring the stinging pincers as he pulled out lobster after lobster. Many of them needed to be released because they were female or too small, but he still managed to catch way more than usual. 

Then, just before daybreak, Izuku slipped away from his friends again. He swam back to the island of reef where the mermaid had found him. He took the biggest, healthiest looking lobster from his bag and killed it with a small stab to the base of its carapace. Then he left it at the entrance to the mermaid’s den. 

Izuku was back before his friends ever realized he was gone. 

—

Mermaids were incredible. 

Izuku had brushed it off with Uraraka that morning, but now, back in the solitude of his own home, he paced back and forth across the floor, his mind running a mile a minute. 

The mermaid was at the front of his mind, of course. Izuku couldn’t stop thinking of their song, or the way their body felt against his own in the darkness, or even the fun bubbling-feeling that had spread in the wake of their touch. 

Lurking behind that though, was the undeniable factor of how long Izuku had stayed under the water for. Izuku could hold his breath for about a minute, maybe 90 seconds if he really pushed himself. 

But if Izuku’s internal clock was anything to go by, he guessed that he’d been under the water for about a minute before the mermaid had shown up, then it had been another several minutes after Izuku clicked his light off that the mermaid got close to him. Then, honestly, he had lost all sense of time. The mermaid could have been pressed against him for seconds or hours. 

All in all, though, Izuku guessed that he’d been under the water for about ten minutes. 

So the mermaid had let him… what? Hold his breath for longer? Had it been the song that did it? Nothing else really made sense. It wasn’t like Izuku’s body was capable of that. At least not on its own…

Izuku’s strange dream from the night before jumped to mind, but he dismissed it quickly. 

Izuku itched the back of his hand, lost deep in anxious thought. 

His eyes fell upon the conch shell placed on his desk. He studied it for several long moments, some of his anxiety melting away as he traced its complex shape with his eyes. 

Maybe…

Unconsciously, Izuku brought his bracelet up to his face and pressed his mouth against red sea glass at its center. The last of Izuku’s anxiety melted away, only leaving behind the pleasant feeling of bubbles on his lips. 

—

The next day, Izuku turned his head for one moment to talk to a fellow surfer. When he looked back, a perfect, bleached sand dollar sat between his knees. 

Izuku picked it up with delicate fingers. His heart began to pound. Could it really be…?

After yesterday, Izuku had been forced to consider that the conch and the bracelet were related to his mermaid. 

Nothing in any book or scientific journal he’d ever read mentioned anything about mermaids leaving gifts for people, but Izuku still couldn’t shake the idea. 

He brought the sand dollar up to his lips and pressed a soft, tremulous kiss to the center of its shell, over the heart of the skeleton flower. 

His lips began to tingle. 

And Izuku got the intense urge to eat it. 

So he did, biting down hard onto the outer shell, breaking off a chunk of the delicate skeleton. It crumbled like sand between his teeth and something oily in the texture made the slide down his throat easily. In another two bites, the skeleton was gone. 

Izuku licked his lips. His mouth felt like it was full of bubbles. 

—

That night, Izuku dreamt of the mermaid. He’d been having strange dreams since he first found—or was given— the sea glass, but this one was different. In the dream, he was back with the mermaid… but he was a mermaid too. His hands looked as if they’d been dipped in a green to match his hair, scaled and slightly clawed. Gills rushed cool water under his ribs, and his legs were long and finned.

The other mermaid— his mermaid—wound their way around Izuku’s body in a tight embrace. They were singing again, the sound low and crooning. Izuku kissed the mermaid’s throat and wound his hands through their soft hair. 

The mermaid hummed in encouragement, winding their tail back around one of Izuku’s legs. “Izuku,” The mermaid whispered, the song breaking off into a moan. Izuku realized that he had a hand under the mermaid’s navel and was pushing between soft folds of scaled skin to…

Izuku woke up with a gasp. 

He was covered in sweat, but felt cold. For a moment, he wanted nothing to be back in the dream. Back there. With his mermaid. Then bile rose in his throat. 

Fuck. 

Izuku had one amazing encounter with an incredible, sentient being, and he freaking fetishizes it? Yikes. Izuku ran a hand down his face, feeling disappointed in himself. 

God, the dream had felt so real though. The sexy bits, yeah, but then the feeling of water over his gills too, and the sound of the mermaid saying his name…

Izuku’s dick twitched in his shorts and he cursed, grabbing it as if that would help. Maybe he could just take the edge off a bit… No. Izuku shook his head firmly. I’m not going there. 

He chastised himself all the way to the bathroom, waddling like a stupid, horny duck. Sure, mermaids were depicted as sexy and alluring in most media, but Izuku didn’t even know for sure if this mermaid was a woman or man, or neither, or what they even looked like!

Not that gender mattered to him, and while something told Izuku that the mermaid was almost certainly gorgeous, it was really the principle of the whole thing.

But then again… 

Izuku paused in the bathroom, enjoying the way the darkness of the windowless room pressed in around him. If he held still, he could almost convince himself that he was back there, under the water, waiting for his mermaid to come find him again… 

Izuku shivered, remembering the ghosts of touch across his torso and stomach, the feeling of a webbed hand in his own, the press of a cheek to his collarbone, and the warmth of lips to his throat…

Fuck. 

Fuck! 

The mermaid had kissed him! They had actually pulled him close—held him as if he were a lover—and pressed their lips to his skin. 

Izuku’s heart, stomach, groin, everything— throbbed. He staggered forward slightly, catching himself on the edge of the bathroom sink and hitting the wall. His shoulder found the light switch, and, in a direct recreation of his time under the water, the space flooded with a sudden light.

“Fuck…” Izuku groaned again, covering his eyes. Slowly, eyes watering, he squinted through his fingers. Shit, I feel like I’m going insane… He put his hands down and sighed, reality reestablishing itself around the bright immediacy of his bathroom.

Izuku turned, intent on taking a cold shower.

And he froze. 

There was… something strange in the mirror. 

Slowly, Izuku raised his arms above his head. There, just under his second and third ribs on each side, two angry, puffy lines cut across his torso. 

Just where his gills had been in the dream. 

“What…” Izuku breathed. He reached out and brushed a fingertip over the top line on his right side and winced. It felt really tender. As if he’d cut himself and the wound had become infected. Only not, because it didn’t feel like an infection but rather like his body was… 

“Changing…” Izuku whispered. Opening. 

He made eye contact with himself in the mirror, unsurprised to find that his eyes were shiny with tears. What was surprising was that his cheeks were already wet… or no. Izuku let go of the lines on his ribs to lean forward. Dusted across his cheeks, just over his freckles, were… scales. 

Tiny, translucent, sparkling scales. 

Izuku suddenly smiled, chest heaving around a sudden onslaught of intense and manic joy. He wanted to scream, he wanted to laugh. But mostly, he wanted to cry from sheer relief.

I never needed to worry. The mermaid is already calling me back…

—

The scales under his bracelet were green.

The first bus of the morning left before dawn and had barely anyone on it, so Izuku felt comfortable examining his skin under the flashing lights of the passing city. 

When he really thought about it, Izuku realized that his skin had been itchy lately. Especially under the bracelet, but he’d never once thought about taking it off and had in fact completely dismissed the feeling. 

Now though, as Izuku itched what he could now see was a whole brace of budding scales across his hand, he paid more attention. Starting under the piece of red sea glass, the scales were a dark green. They slowly lightened until they turned clear a few centimeters away from his bracelet. Or maybe it would be more accurate to say that the scales were in the process of darkening and just hadn’t yet… because that’s what it looked like. 

As if the scales were spreading, darkening as they matured.  

Izuku pressed his lips to the red bead of the sea glass. He recalled the crunch of the sand dollar under his teeth and the oily sting in its flavor.

Should I eat this too…? He wondered, excitement coursing from his palpitating heart all throughout his body. But no. The bracelet was clearly doing its job, whatever the end goal was. 

Hopefully, his dad would have some answers. 

—

Toshinori Yagi was not Izuku’s biological father, but he was his dad in every way that mattered. Izuku had met the retired surfer shortly after he’d moved into the Alliance Waves house. 

Yagi had taken Izuku under his wing and with his tutelage, Izuku had been well on his way to qualifying for some of the biggest surf competitions internationally, let alone the country. 

Then, when Izuku’s mother had her accident and Izuku had requested to take some time off to go care of her, Alliance had shown Izuku the door… and Yagi had opened his. He moved Izuku and his mother into his own home, helped Izuku take care of Inko all throughout her recovery, and had trained Izuku straight into the championship title. 

Izuku had cried like a baby at his parent’s wedding. 

More recently, when Izuku had announced that he wasn’t interested in competing anymore and wanted to take his life in a new direction, Yagi had just smiled and said he’d support Izuku with whatever he wanted. Izuku sometimes felt bad that he still didn’t know what that direction was, but Yagi had never rushed him. 

Toshinori Yagi was, quite literally, Izuku’s superhero. 

If anyone could help him understand what was happening, then it was him. 

And sure enough, when Izuku knocked on his parent’s door at 6:30 in the morning, Yagi was ready with a hug and two cups of fresh coffee.

“I had a feeling you’d drop by today,” Yagi smiled, patting Izuku on the shoulder and leading him inside. They made small talk over the first sips of their coffee and Izuku listened to the comforting sound of his mother getting ready for her day just down the hall. Before she could come out and join them, Yagi probed Izuku into talking. 

“So what’s on your mind, Izuku?” He asked. “You have a very confused look about you.” 

Izuku opened his mouth, then closed it. How did someone ask their dad what to do when they thought they might be transforming into a mermaid? Even just thinking that sentence made Izuku feel insane. 

Yagi waited patiently, sipping his coffee in contented silence. 

“Have you ever…” Izuku sighed, fidgeting in his chair. “Have you ever heard of a… a mermaid… giving a human a gift?” 

“Hmm.” Yagi thought about the question over a long sip. “Yes,” he finally nodded. Izuku’s breath hitched in his throat. “It sounds like you’re asking me about The Mermaid’s Bride.”

“The… mermaid’s bride…?” Izuku asked, a dark flush rising to cover his cheeks. 

“Mhm. It’s an old folktale around here. My mother first told me the story when I was a boy. Would you like to hear it?” 

“Y-yes!” Izuku nodded eagerly, scooching his chair closer.

“So… a long time ago, a mermaid moved into the local waters. Not the mermaid we have now, of course, but perhaps one of their distant ancestors. The people who lived here at the time rejoiced and celebrated, because everyone knows that a mermaid means healthier reefs, healthier fish, and more food for everyone.” 

Izuku nodded eagerly.

“Well, there was also a young woman who lived in a fishing village along the beach. Her name was Shinju. She was a beautiful young lady and a powerful fisherwoman. Many people asked for her hand in marriage, but she rejected them all. 

“One day while hunting on the reef, however, Shinju dropped her spear. That was no problem, as she merely swam down to the bottom to pick it up. When she returned to the boat, however, she noticed that a delicate necklace of strung Puka shells was wrapped under the point. The necklace was beautiful, so Shinju started wearing it from that day on, even though she had no idea where it came from.”

Izuku felt his mouth go dry. His heart picked up a beat in his chest and his hand curled over his bracelet. 

“After that, many more gifts came to Shinju from the ocean. Shells and pearls, yes, but also the most delicious fish swam into her net as if lured there. She gained the ability to stay underwater for longer and longer periods of time, and eventually she was able to see as clearly under the waves as she could above them.

“Finally, after months of this, Shinju announced that she wished to marry her gift giver. She asked each person in the village if they had been the one to lure fish into her nets and hide gems and shells for her to find but of course, everyone denied giving her the gifts. 

So Shinju went down to the beach by herself on a quiet, foggy morning. She waded into the waves called out, asking for her love to show themselves. Finally, they did.” 

“It was the mermaid?” Izuku asked, his eyes wide. 

“It was the mermaid.” Yagi confirmed, nodding. He took another sip of his coffee. 

“So… what happened next?” Izuku probed. 

“They married, of course.” Yagi said. “The entire village came down to the shore, and Shinju married her love in the soft foaming water. Then she followed them down into the reefs, and according to the legend they had a lot of children; all of whom went on to protect new reefs.”

“Wait so… Shinju was able to live with her mermaid? Under the water? So she became a mermaid too?” 

Yagi shrugged. “Some versions of the story say that she became a mermaid and eventually lost her ability to return to land, while others say that she remained human but could breathe underwater, and finally other versions say that she became something between a mermaid and human.” 

“Oh, wow…” Izuku looked down, fiddling with his hands. He felt embarrassed to ask, but he had to know. “Dad is… is Shinju’s story real?” 

Yagi considered Izuku with a long, fond look, his coffee forgotten. “I don’t know, my boy. But I know that many coastal towns like ours have similar folktales and legends. And I know that mermaids have been revered as sacred for millenia—not just because of their utility to our fishing, but also because their history and nature are inextricably intertwined with our own. 

“Mermaids and humans both come from the ocean. A long time ago, we left the ocean together. Humans remained on land, but mermaids eventually elected to return. It really wouldn’t surprise me if mermaids still remembered how to return us home.”

—

Izuku knew what he had to do. 

Maybe he was crazy. Maybe eating that sand dollar had given him some weird disease. Maybe the mermaid’s bride was nothing more than a bedtime story for fussy toddlers. 

But maybe… maybe none of that was true. 

Maybe Musutafu’s mermaid had fallen in love. And maybe Izuku had fallen in love right back, tumbling head over heels the moment a scaled hand touched his own, deep in the dark under the waves.

He hurried himself out the door, already planning the fastest route to the beach from his parents’ house. Yagi stopped him for just a moment.

“You will come back and visit us, won’t you?” He asked, his eyes worried and knowing, but understanding, too. 

“Of-of course I…,” Izuku trailed off. Could he really make any promises right now? Everything was happening so fast… Izuku squeezed his eyes shut and wrapped a hand around the slowly growing band of green around his wrist.

“I’ll try,” he finally whispered.

“That’s all I can ask. And Izuku?” 

“Yeah, dad?” 

Yagi shook his head, a gentle smile stretching across his face. “Just… I always knew you were meant for something incredible. Good luck, son.”

—

The water was calm. Not a good day for surfing, but a great day for paddle boarding. Izuku had decided to head to the beach where he and his friends had gone lobster hunting. Now that he was here though, standing atop the still water and looking down at the reef far below, he felt a bit silly. 

I really, really hope Shinju’s story is true. 

Izuku sighed and plopped down on the paddle board, splashing his legs into the water. His knees felt wobbly and his stomach was full of butterflies. He’d better sit down for this. 

“Alright…” He said aloud, voice shaking but gathering strength as he went. “If you can hear me… I’ve been receiving quite a few gifts… Um, this bracelet… Which is beautiful, by the way, and a few shells. I ate one of them…” Izuku looked down at the bead in his bracelet, feeling self-conscious. 

“I also can hold my breath underwater for a long time now, and I guess that’s your doing. Um, it’s really cool, obviously! I’m not complaining! I am wondering how you even did that, though. I was thinking that maybe that oily texture I kept feeling on the glass and the shells might have been causing the scales, but even that seems far-fetched. The whole increased-lung-capacity thing is insane, and don’t even get me started on the gills. If they even are gills! I dunno maybe I have an infection—”

“Do you always talk this much?”

Izuku jerked his head up. His jaw dropped. 

There, perched with one arm at the end of his board, was the most beautiful being Izuku had ever seen. 

The mermaid’s hair was as bright and fine as spun gold and his eyes were drops of liquid fire—glowing like magma deep under the cracks in the ocean. Orange scales brushed across his cheekbones and framed his eyes. When he smiled, twin sets of fangs shone like pearls in the sun. 

“I…” Izuku’s mind spun for something, anything to say, but he pulled a blank. 

“Oh? At a loss for words now, I-zu-ku~” 

The mermaid pulled himself up onto Izuku’s board gracefully, leaning forward onto thick, strong arms. His tail was such a deep red that it was nearly black and his fins were bright orange, accented in green. The red scales on his fin sparkled this way and that in the sun, reminding Izuku once more of a lava flow. 

Is this really happening? Is this REALLY happening?!

“You… you know my name?” Izuku asked, struggling to put more than two coherent thoughts together. 

There’s no way. 

“Of course I do.” 

“And you… you’ve been giving me things?”

“Yep.” The mermaid inched closer, bringing his hand up to caress across Izuku’s cheek. Izuku leaned into his touch automatically, resisting the urge to close his eyes.

…This is really happening.

“What’s your name?” Izuku asked breathlessly. 

“Katsuki,” The mermaid said. 

“Katsuki…” Izuku loved his name. It was powerful and fitting. But the longing melting his heart yearned for something a little different. “Kacchan?” He asked, silently begging the creature before him to accept the raw affection in the offered name. 

Katsuki’s eyes softened. “Sure,” He agreed. “For you, only, I’ll be your Kacchan.” 

That was all Izuku wanted. 

Slowly, unwilling to scare him off, he reached to pull Katsuki towards him, placing a careful kiss on his lips. 

For a moment, Katsuki didn’t move. A bolt of fear cut through Izuku’s brain. He wondered if he’d misunderstood something, or if the mermaid would even know what kissing was… But he needn’t have worried. 

Because Katsuki lunged forward a second later, deepening the kiss. He threw his arms around Izuku’s shoulders and wriggled straight into his lap. The paddle board splashed and rocked with the motion, but they managed to stay aboard, somehow. 

Katsuki broke away after just a moment, grinning maniacally. Izuku looked up at him in unfiltered awe. 

“Oh, you are mine!” Katsuki said, chest heaving around a low growl. He ducked down to bite and gnaw at Izuku’s jaw, seemingly unable to restrain himself. His fangs broke Izuku’s skin just slightly, and Izuku shivered, tilting his head back to give Katsuki all the room he wanted. “Mine, mine, mine,” Katsuki crowed, sounding delighted. His tail wound around Izuku’s legs, pinning them together, and his arms wrapped around his torso to pull him closer. 

“Yeah,” Izuku agreed automatically, feeling a little dazed. “I’m yours.” 

Katsuki kissed him again. “Mmf,” Izuku mumbled. He could taste his own blood on Katsuki’s lips, but also more of that same sweet oil he’d eaten from the sand dollar. Izuku shifted his hands down to Katsuki’s waist. He squeezed, his heart racing. Fuck, he wanted to touch him everywhere.

“Kacchan,” He mumbled, “You taste…” 

“Good?” Katsuki guessed, smirking as Izuku took the opportunity to return a kiss to his throat. “Have you gotten used to my taste already, nerd? You know I never expected you to come find me this quickly! I thought you’d hold out for another few courting gifts at least… but I guess you want me pretty bad, huh?”

“So I was tasting you? In the sand dollar?” Izuku asked, ignoring the other question. It should be pretty obvious how much he wanted Kacchan—the mermaid was sitting in his lap, after all. As if reading his thoughts, Katsuki encouraged Izuku’s wandering hands with a small roll, pushing Deku’s hands down onto his tail, and grinding shamelessly into his hard groin. 

“Fuck!” Izuku gasped, hands scrambling to pull Katsuki even closer. 

“Yes,” Katsuki laughed, answering his question even as he ground down again. “Though I never expected you to eat the sand dollar, you fucking weirdo.” 

“Oh, I’m sorr–”

“Don’t you dare apologize,” Katsuki interrupted. “It was fucking hot.” 

Izuku’s face flushed. “You think I’m hot?” He asked breathlessly, hands squeezing and testing the firm but plush muscle around Katsuki’s hips. “Is that why you started giving me gifts?” 

“I think you’re a lot of things.” Katsuki tilted his head up, biting another kiss onto the underside of Izuku’s throat. 

“Ah, Kacchan…” 

“You’re hot. You work harder than any human I’ve ever seen. You make the people around you laugh and you inspire them to be better. You’re honest, and sincere. I watched you win that surfing competition last year. You have no idea how loudly I cheered for you. I wanted to claim you then, but the reefs couldn’t support more of us yet. But then I saw you working with all your students and I couldn’t wait any longer. I knew another human would come claim you if I waited too long… Plus… I’m impatient. I want your guppies.”

Guppies?

“You… you’ve been watching me that long?” Izuku asked, setting aside that last thing for now. His hands curled around Katsuki, pulling him a little closer. 

“Does that bother you?” Katsuki asked, eyes gleaming. Judging from the expression on his face, he already knew the answer. 

Izuku shook his head. He ducked back down to kiss him again. If anything, he felt pretty hot under the metaphorical collar just thinking about it. The mermaid of Musutafu—the prettiest creature in the world— had been admiring him? Wanting to claim Izuku as his own? Izuku traced his hand under Katsuki’s jaw, across the fins of ears, and down to his waist.

“That’s… thank you, Kacchan.” 

“Of course,” Katsuki murmured. “I knew the moment I saw you that you’d be mine, nerd.”

Oh my god, yes, please.

Katsuki laughed, wriggling atop Izuku’s dick, and Izuku realized that he’d accidentally said that aloud. “I already said you were,” Katsuki teased, “There’s no need to beg.”

Izuku felt a flush of embarrassment hit his cheeks, but covered it up by kissing Katsuki again. His lips were so fucking soft. Izuku felt almost bad for his own salt and sun chapped lips, but Katsuki didn’t seem to mind, moaning quietly as Izuku nibbled against his mouth.

More, Izuku’s brain demanded, urging him to push Katsuki back down onto the board, to see if his nipples were soft too, to see if the translucent scales on his upper body would still let Izuku mark him up, to see if his dream had been accurate, and Izuku really could push between folds of scales below Katsuki’s navel…

“Wait,” Katsuki gasped, “Stop.”

The soft command stalled Izuku immediately. He sat up from where he’d nearly succeeded in pushing Katsuki back down onto the board. 

“Hey, relax,” Katsuki protested, wrapping his arms around Izuku’s neck. “I just wanted to make sure we’re on the same page, dork. I’ve been courting you, y’know? I want you to be my mate.”

“Yeah…” Izuku confirmed. Hearing Katsuki say it out loud left him breathless.  

“But mermaids aren’t like humans,” Katsuki continued, his gruff voice falling into something gentle and almost melodic. “We only take one mate. Ever. If we stop now, and if you throw your gifts away, you’ll eventually turn back to normal. But if we keep going…” 

“There’s no going back.” Izuku guessed.

“Yes,” Katsuki confirmed. “And you’ll change. You’ve already started, but once we’re mated the changes will speed up. It might even hurt a little bit, but I’ll do my best to soothe your aches, okay? You just… I need to hear you say it. I need you to agree, knowing that… that you can’t go back.” 

Katsuki’s eyes were worried as they met Izuku’s own, and a small part of Izuku’s heart broke just then. He wanted to scold himself for even giving Katsuki the smallest reason to doubt him.

“Izuku?” Katsuki prompted, His webbed hands rubbing soothingly into his hips and legs… and then ventured enticingly close to his ass and groin. As if Katsuki was trying to both let him decide, while also doing his best to tempt him.

Kacchan is so fucking cute, Izuku thought. He leaned down to kiss Katsuki gently, purposefully holding back and instead pouring every ounce of tenderness and softness that he could into the kiss. 

Katsuki kissed him back just as gently. 

Somewhere near the cliffs, a gull cried. A wave hit the rocks, and the ocean lapped at the edges of the paddleboard. Izuku’s favorite place had always been the ocean, but he’d never once thought that he’d ever be a part of it. 

I want this, Izuku thought, brushing his thumb across the soft sharpness of Katsuki’s cheekbones, and feeling the firm give of the scales under his eyes. He pulled away, breaking the kiss with a quiet smacking sound. 

Below him, Katsuki looked… stunned. He stared at Izuku with a kind of dazed affection that made Izuku want to… Well. He should probably give Katsuki a proper answer before doing that. 

“So if I go with you… I’ll turn into a mermaid?” Izuku asked, pushing a strand of wheat-golden hair behind Katsuki’s ear. 

“If… If you want to,” Katsuki murmured. “I think we can get your gills to open today, but any other changes will be up to you. My dad was like you—used to be a human. He decided to keep his legs, but I’ve met others who decided they wanted more…”

“Oh wow…” Izuku’s eyes grew wide with wonder. So Shinju’s story was true. Mermaids choosing human brides was apparently something that they just… did. Izuku felt overwhelmed, incredibly excited, and honored. 

Katsuki squirmed until he slipped off of Izuku’s lap. He looked up at Izuku with half-guarded vulnerability. “So?” He asked, “Do you accept my courting, Izuku?” 

“Yes,” Izuku smiled, the truth of what he wanted spilling from his lips. Even if Katsuki hadn’t been promising Izuku the future of his dreams, Izuku knew he would have accepted.

Izuku had never believed in love at first sight… Until now. Seeing Katsuki at the end of his board had tilted Izuku’s world on its axis. Even before that… perhaps he’d fallen for Katsuki at first touch, or at first embrace. Deep down, Izuku had known from the moment Katsuki’s hand found his own down in the dark that he’d do anything to be with Katsuki again.

Beyond that, even, was the sheer awe Izuku held for Katsuki. Izuku moved to this town to pursue a career in pro surfing, but even after he quit competitions, Izuku hadn’t been able to stand the thought of leaving this stretch of ocean. Though he hadn’t realized it at the time, Izuku realized that he hadn’t been able to stand the thought of leaving Kacchan. It would have made sense to return to the city to study, but then he wouldn’t have been able to continue watching the way the reefs built up, flourished, and exploded with life under Katsuki’s care. 

So… perhaps this wasn’t so sudden after all. Katsuki claimed that he’d been watching and falling for Izuku all this time, and though he hadn’t been watching him directly, Izuku had been seeing Katsuki’s work, and he’d been falling for him through that.

“Yes, please, Kacchan. I want to be yours. I want to help you. I want to join you, wherever you are.” 

Katsuki flashed him a brilliant, delighted smile. 

“There’s just one thing,” Izuku continued, hesitantly. Katsuki’s smile dimmed. His brows dipped into what Izuku was beginning to suspect was a signature look for him. 

“What’s that?” Katsuki asked, pouting.

Oh my god, he’s so fucking cute, what the fuck.  

“Um…” Izuku struggled to remember what he wanted to say. “Right. So, the word “mate” seems to imply… Uh, you know. And, well, you mentioned wanting ‘guppies’ earlier, so uh…”

“Spit it out, Izuku,” Katsuki frowned.

“Babies.” Izuku blurted. “You want babies. But you see the thing is—I don’t know how it works between mermaids, but I’m a man, well, we’re both men. I think. And um, I can’t… have… babies?” 

Katsuki squinted at Izuku in sudden confusion. 

“You can’t have them at all?” He asked. 

“Well I—! I mean I can, um, participate in the process…! But I can’t… carry…? The babies?”

Katsuki burst into laughter, the smile from earlier returning to his face, tenfold. “Fuckin’ hell, Izuku! Are you trying to explain to me that you’ve got a dick?!” 

“Well!” Izuku spluttered, “I mean—!” 

“Relax, nerd.” Katsuki soothed, still laughing. “I know what I’m working with.” He smoothed his hand from Izuku’s chest down to his stomach. Izuku’s breath hitched as Katsuki’s hand slipped down to fondle him through his bathing suit. “And I can make up for what you silly humans lack, alright?” He laughed again, clearly amused. “I can’t imagine having only one set… that’s gotta be weird.” 

“Nngh,” Izuku groaned, leaning down to press his face into Katsuki’s shoulder. Katsuki continued to pet his dick outside his shorts. 

“N-no fair, Kacchan,” Izuku gasped. 

“Hm?” 

“I don’t—I don’t know what I’m working with.” 

“Oh? D’you want me to show you?” Katsuki leaned up, nipping at the lobe of Izuku’s ear with his fangs. “Want me to show you how to make babies, Izuku?” 

“Holy fuck,” Izuku gasped. The shot of arousal from his gut to his groin was so intense that he went dizzy for a moment, surging forward to pull Katsuki into a harsh kiss. Like when Katsuki had given him that sand dollar, suddenly every instinct in Izuku’s body was screaming at him to devour.  

Izuku had always known that he wanted kids, of course. But it had been a thought for the future. Something distant. Now though… 

“Yes,” He begged, sliding his hand down the front of Katsuki’s tail, under his navel. “Show me, Kacchan.” Show me how to make you feel good. Show me how to get you pregnant. 

“A-ah,” Katsuki gasped and Izuku chased the sound, ducking to bite across his collarbones even as he pet harder in the spot that had made Katsuki moan. “You-you’ve got it,” Katsuki hissed, “J-Just keep touching me there…”

Izuku stroked two fingers up and down, marveling at the way Katsuki’s body seemed to soften under his touch, each pass drawing a louder gasp from the mermaid's mouth. Until finally, Izuku’s fingers slid down into something warm. 

“Mmm…” Katsuki moaned, tilting his head back against Izuku’s shoulder. Izuku smiled, shifting slightly on the board to better support his weight. He dipped his fingers into Katsuki’s warmth again, easing in slowly because his pretty mermaid was still in the process of opening up for him. Each press of Izuku’s fingers widened his slit more and more. 

“Fuck, yes, there we go,” Izuku murmured, pressing a hard kiss to Katsuki’s cheek. “Look at that, fuck, you’re so gorgeous.” 

“Ah… Glad you—glad you kn-know it, mnh! Izuku!” 

Izuku licked his lips. A thin, tentacle-like appendage poked out of the top of Katsuki’s slit, eagerly wrapping itself between Izuku’s fingers. 

Damn, Katsuki was beautiful. 

Izuku couldn’t hold himself back anymore. He ducked down, sending the paddle board rocking in a precarious motion, and buried his face into Katsuki’s slit. 

The mermaid cried out, his hands immediately burying themselves in Izuku’s hair. “Th-there! Oh, fuck, Izuku! There, r-right…!” 

Izuku sucked, drawing as much of Katsuki’s champagne slick into his mouth as he could. At the same time, Katsuki’s tentacle (his dick, Izuku was fairly certain) writhed around inside Izuku’s mouth, pretty much shoving itself down his throat. It wasn’t particularly thick, so Izuku didn’t choke, but he did his best to suckle at it, applying gentle pressure and swallowing.

The sounds dripping down from Katsuki’s mouth were divine. He pulled at Izuku’s hair, tugging him this way and that, hands trembling as Izuku’s licked down into his slit. He let Katsuki’s tentacle rub across his soft palate while he kissed and lapped at the soft skin inside his body, making sure to drink every drop of Katsuki’s overflowing slick.

Kacchan tastes so good, Izuku thought. He did—it was surprisingly sweet, a little tangy, and had echoes of the oily taste from the sand dollar. Izuku thought about what the sand dollar and other gifts had done to his body, then thought of what Katsuki’s slick would probably do to him… and he redoubled his efforts, bullying his arms under Katsuki’s hips and yanking Katsuki up into the air, burying himself that much deeper into his cunt. 

More, more, more, he thought, sucking at his dick, pulling back to lick the leaking juices from the edges, and then going back in, plunging his tongue inside until he found the spot that made Katsuki’s slick pour. 

“Oh f-fuck!” Izuku tuned back in as Katsuki’s cries sudden;y warbled close to a scream, his voice tight with ecstasy. “I-Izuku! Hold on, hold on! I’m–I’m n-not, I can’t…! I can’t hold back, I…!”

Izuku wiggled his shoulders, delighted. He pushed his tongue inside Katsuki as far as he could manage, finding that spot again, and probed it hard with his tongue, pressing rhythmically, even as Katsuki’s dick began to throat-fuck him.

“There, there,” Katsuki wailed, “Right there! D-Don’t move, Please, please, right there…!” 

He went rigid in Izuku’s arms, trembling violently even as his voice careened off into a warbling, inhuman cry. Something hot and bitter burst across Izuku’s tongue just as more slick flooded his mouth. Izuku suckled Katsuki dry, only leaving when the mermaid whined and began to push him away. 

“Mm,” Izuku said aloud, sitting up. He licked his lips again, chasing the dual flavors of Katsuki’s cum and slick. “Kacchan tastes really good…” 

Katsuki stared upward, unseeing and panting hard. “V’never… come from both… at once before…” He murmured. 

Izuku’s chest bloomed with pride. He leaned down to press a flurry of kisses to Katsuki’s cheeks. “I’ll make you come like that everyday, if you want,” He promised.

“Do you… mean that?” Katsuki asked, his eyes refocusing to meet Izuku’s.

Izuku grinned. “Course I do, sweetheart! Anytime you like.”

Katsuki groaned and Izuku felt the end of his tail wrap around his ankle. “I am definitely taking you up on that,” He agreed. “In the meantime though, I haven’t made good on my promise yet.” 

Katsuki’s hands slid back down to the thin material of Izuku’s swim shorts. Izuku swallowed as Katsuki slowly fished him out of the material. His dick bounced when it was free, and Izuku flushed in embarrassment over how hard he’d gotten. Pre dripped from his tip like a leaky faucet. 

“Fuck yeah,” Katsuki murmured, using one hand to pump Izuku up and down, spreading pre all over the shaft. With this other hand, he dipped down inside his slit, covering his fingers with slick. When he pulled slick webbed fingers back out of himself and wrapped them around Izuku’s dick, Izuku nearly came on the spot. 

“Oh f- fuck!” He hissed, knocking Katsuki’s hand out of the way to squeeze around the base of his dick, hard. He managed to stave off the impending orgasm, but only barely. Katsuki cackled under him and continued to spread more of his slick across Izuku’s dick, heedless of his protests. 

“Don’t worry baby,” He cooed, “We’ll work some stamina into you.”

Izuku growled in the back of his throat, a little affronted at the insinuation. His stamina was fine, thank you, Katsuki was just that sexy. 

A moment later though, he startled, picking his head up off of Katsuki’s chest. Katsuki looked just as surprised as him. A slow grin spread across his face. 

“Not a very human sound you just made there, Izuku baby. Fuck, you’re just takin’ my courting gifts and runnin’ with them, ain’tcha?” 

“Mm.” Izuku tried the growl out again, liking the way it rippled out of his throat. Then he tried one of the purrs he'd heard from Katsuki, and finally, a croon. 

The moment the croon left his throat, Izuku’s leg was suddenly a lot wetter. Katsuki blushed fiercely, and Izuku crooned louder, delighted. 

“Enough,” Katsuki hissed, pulling him closer. “Now you’re just wasting my slick. Hurry up and fuck me already.” 

Between all the kissing and teasing, Izuku had somehow managed to lay down lengthwise on the board, with Katsuki underneath him. Paddleboards were fairly steady, but Izuku was still surprised that they hadn’t capsized yet. He attributed it to Katsuki’s tail—the significant bulk of which was still under the water, no doubt helping keep them steady. 

“Your wish is my command,” Izuku agreed, brushing a kiss across Katsuki’s lips. 

Katsuki huffed. “And don’t you forget it,” he grumbled, but used one of his hands to reach between Izuku’s legs and guide him closer. Katsuki tried to push Izuku inside, but Izuku held back, electing to rub the tip of his dick against Katsuki’s retreating tentacle and humping against the soft, soaked folds of Katsuki’s slit. 

“Wh-what are you waiting for?” Katsuki asked, breathless. “J-just stick it in, already.” 

“Be patient, sweetheart,” Izuku soothed. “I wanna take my time.” 

“But why?” Katsuki whined. 

Izuku smiled. “Because it’s my first time making love to you.” He said, kissing Katsuki’s swollen lips. “And I want to remember every moment.”

The look Katsuki gave him was there and gone in an instant, but that was fine; Izuku had seen the raw vulnerability and wonder there as plain as day. 

“Fuck, Izuku,” Katsuki whispered, his eyes wide. “Please?” 

Oh wow. 

Izuku knew he’d never be able to deny Katsuki anything, if he looked at him like that. 

“Alright Kacchan,” he agreed, kissing his temple. “Remember to breathe, okay?” Slowly, Izuku pressed down, easing his tip into the swollen flesh of Katsuki’s slit. 

“Fuck!” Katsuki hissed, tossing his head to one side, then the other. Katsuki’s body shook around the intrusion; he seemed to be simultaneously trying to pull him closer and push him away. 

“Shh…” Izuku soothed, crooning low in the back of his throat. “You’ve got to relax, sweetheart.”

“I-I c-can’t,” Katsuki whimpered, every ounce of his bravado draining away. “Y-you’re too big!”

“I’m not,” Izuku denied, reaching down to pet the tentacle at the top of Katsuki’s slit. “You can take me, Kacchan. I know you can. Just take some deep breaths for me, okay? There’s nothing to be scared of… It’s just you and me, alright? I’ll go slow.” 

Katsuki whined, but began to relax as instructed, his chest heaving with his breath and his stomach clenching.

Izuku waited until the trembling stopped and then eased his way in with slow, building thrusts. He crooned in delight and pet against Katsuki’s dick until his hips were finally pressed flush to Katsuki’s tail. 

“F-fuck,” Katsuki gurgled. His head tipped back against the paddle board and the end of his tail wrapped around Izuku’s ankle like a vice. 

“Kacchan is amazing,” Izuku praised, pressing a line of kisses to his jaw. “You did really well, sweetheart.”

Izuku expected something snarky in response, but his heart filled with joy when Katsuki just gasped out a small, “Really?”

“Yes, really.” Izuku said warmly. “How are you feeling?” The slow, focused process of getting inside Katsuki had taken the edge off of his own impending orgasm, but he didn’t think that it would take that long to get close again. Not when Katsuki’s insides were fluttering against him like that. 

“Mm…” Katsuki dragged his hands up his own body, tracing small circles across his chest and nipples. Izuku watched their path with hungry eyes, memorizing them for his later use. He wanted to know everything that Katsuki liked. How he touched himself especially. 

“I feel full,” Katsuki mumbled. “I feel…” 

He rolled his hips in a small, careful circle. Izuku held a growl between his teeth. 

“I feel… good…” Katsuki whispered. 

That was better than permission. Izuku pulled back slowly, looking down to watch in awe as slick clung to his dick as he went. When only the tip was still inside, he pushed back in. 

Izuku knew that Katsuki’s tiny, drawn out groan would haunt him for the rest of his days. He could hear that sound everyday and never grow sick of it. 

Izuku set a slow, steady rhythm, delighting in each moan and the wet sounds their bodies made when pushed together. 

“More,” Katsuki gasped, quickly. “C’mon, Izuku, gimme more. I can take it.” 

“Of course you can,” Izuku agreed, but he didn’t speed up, too busy loving the way Katsuki’s hips jerked to try and give himself the friction that he needed. 

(Somewhere in the back of his head, Izuku allowed himself to be surprised over how much of a tease he apparently was. No one had ever brought out this side of him before.) 

“Izuku!” Katsuki cried, pricking the sharp tips of his claws into Izuku’s back. “Come on! Please!” Izuku noted that Katsuki was beginning to tremble again. 

“What is it, Kacchan?” Izuku asked while still keeping the same slow, deliberate pace. He knew what Kacchan was asking for, but he wanted to hear his little mermaid say it.

“F-fuck me!” Kacchan cried, his hips jerking up into Izuku’s, out of rhythm but so, so good, his insides clenching, seeming to draw him deeper with every thrust.

“I am fucking you,” Izuku grinned, pressing an open mouth kiss against Katsuki’s cheek. 

“Fuck me harder!” Katsuki shrieked. “You stupid Deku! Do you really expect to give me guppies like this?!”

The growl ripped itself out of Izuku’s throat like a thunderclap, and suddenly he was slamming his hips forward, fucking into his mate’s slit mercilessly. 

Katsuki shrieked in delight, his voice rising into a victory cry that was frankly adorable. 

Izuku couldn’t even be mad. “Fuck, fuck, you’re so fucking cute,” Izuku grunted, picking up the pace, letting himself finally feel the way Katsuki’s warmth was wrapped around him. “So amazing and gorgeous. God, fuck, I can’t believe you want me.” 

“Hah, ah, ah, f-fuck, Izuku, I really, really do, so please, please…!” Katsuki broke off into a series of whimpers, crying out in time with the slap of Izuku’s hips against his skin, unable to finish his sentence. Not that he needed to. Izuku knew what he wanted. 

“Mine,” Izuku growled, catching Katsuki’s lips between tiny wails. “You’re mine, sweetheart. Mine, mine, mine…!” 

“Yes, yes, yes, yes, Izuku!” Katsuki screamed and arched upward so high that he nearly knocked them both off the paddleboard. They fall back to the water with a splash, but Izuku was far too gone to care about whether or not they might fall. 

Katsuki wailed, his insides clenching and fluttering around Deku’s cock, his hips jerking instinctively to draw out the last of his orgasm. 

Izuku buried his head deep into the warmth of Katsuki’s throat and thrusted in once, twice, three more times, drawing the last one out with a muffled groan and a rough circle of his hips. He came so hard his body shook with pleasure from the root of his hair to the tips of his toes, then back to his fingers, gripping hard onto Katsuki’s wrists. Which… he hadn’t realized he’d captured above his head. 

For a moment, neither of them moved. They just laid there, miraculously still on the paddle board, breathing in the smell of the ocean and each other. 

“...Wow,” Katsuki said eventually, sliding his hands from Izuku’s grip. 

“Wow,” Izuku echoed, smiling, twisting his head to bury affectionate kisses into Katsuki’s throat.

“I knew that it would feel good, of course, but that…” 

Izuku kissed his lips. “I’m glad you enjoyed it, Kacchan.” 

“...You did too, right?” 

Izuku wanted to laugh, but didn’t, already understanding that his mate was a bit sensitive. The last thing he wanted was to ruin the post-orgasm bliss. “Of course, Kacchan. You were amazing.” 

“Good! Obviously! Of course, I’m the best at everything.”

“Mm. Kacchan’s amazing.” Izuku agreed. 

Katsuki flushed in delight, wriggling a little. “Do you… wanna see if it worked?” 

“Hm?” Izuku looked down to where they were still connected. “Isn’t it… a bit too soon to know if you’re pregnant?” 

“Not that,” Katsuki laughed, pushing Izuku gently back. Izuku followed his guidance obediently, watching in utter fascination as he slid out, revealing Katsuki’s cum and slick filled hole. Katsuki pressed two fingers to either side of his slit and within a few moments it began to close. 

“Although I appreciate your enthusiasm, you probably can’t knock me up yet.” Katsuki caught Izuku's eye and winked. “Probably. But I won’t waste anything, just in case.” 

Izuku swallowed down the urge to suggest that they go again right away. Just in case. 

“What-what did you mean then?” He asked instead. 

“...These.” Katsuki sat up. He reached a gentle hand out to caress Izuku’s gills. “They look like they’re ready to open now. C’mon, Izuku. Do you wanna see my reef in the daylight this time? I can show you the home I’ve been building for us. We can try again inside our den too, if you’d like.”

“Yes.” Izuku breathed. “Yes, please. Show me your world, Kacchan.” 

Katsuki grinned. “It’s your world now too, dork.”

Izuku realized he was right. Katsuki’s world was his world, now.

He took Katsuki’s hand, slid the paddleboard’s leash off his ankle, and slipped down into the crystal salt waters. Along his ribs, he felt something flare open, and tasted a rush of salt water so salty and divine it made his head spin. 

“You ready, nerd?” Katsuki asked, holding his hand tightly. 

Izuku smiled, admiring the happy, excited curve of Katsuki’s lips and the way his tail was already coming up to once more twine around his leg.

Izuku took a breath. He looked up at the shining, hot sun above them, then to the towering cliffs purring with the waves, and finally, to the shore in the distance. 

He’d visit, he knew, if just to see his parents again, but he wouldn’t miss it. Not really. He’d been made for this. Made for the water, made to spend his life by Katsuki’s side.

He turned back, and the rest of the world paled in comparison to his mate’s glowing, fierce radiance. Brighter than any sun, stronger than any wave, more alluring than anything the surface had to offer. 

 “I’m ready, Kacchan.”

They didn’t take a breath. They just dove. With Katsuki’s hand gripping his own, Izuku left one world behind for another, and it felt like coming home.