Archive of Our Own

The apartment in Tokyo hummed softly with its usual late‑night quiet. Senku stood by the kitchen counter, fingers twitching slightly as he wiped down a perfectly clean surface. His heart raced. Not from caffeine, not from an experiment gone wrong, but from the knowledge that Gen was waiting for him only a few meters away.

They had tip‑toed toward this moment for days now. Ever since returning from Houston, there had been a new kind of awareness between them. The way Gen’s hand lingered on Senku’s arm a little longer than usual. The way Senku’s eyes tracked Gen’s movements around the apartment, memorizing every small smile, every tilt of his head. The way they sat closer, touched more often, shared quieter laughs. And much to Senku’s frustration, every time Gen joked about a shower, Senku’s brain answered with unhelpfully detailed images.  Even the distant rush of water made his pulse jump. It was illogical, inconvenient, and completely beyond his control.

And tonight the air felt charged. Like a mix of nervousness, restlessness and something... deeper.

Senku drew in a slow breath, bracing himself. It's fine. I can handle this. We can just talk. Or maybe we just kiss. Or maybe-  He cut himself off sharply. No point spiraling.

With a hand pressed briefly to his chest to steady his heartbeat, he walked down the hall to Gen’s room.
A memory stirred in his mind, his father’s voice, low and calm. You and Gen already do that. That’s intimacy. Everything else is optional.

Senku swallowed hard. That conversation had felt a little bit overwhelming back then. Now it felt like a hand at his back, steadying him.

I don’t have to figure it out alone.

Maybe tonight didn’t need a blueprint. Just a beginning.

Gen was sitting cross‑legged on his bed. His hair was still a bit messy from the shower and he was flipping through something on his phone. He looked up immediately when Senku entered the room, a slow grin tugging at his lips.

"Well, well, genius." Gen drawled playfully. "Come to join me on the bed or just here for the delightful company?"

Senku huffed, crossing his arms. "Don’t start."

Gen chuckled softly but set the phone aside, his expression softening. "Hey. You okay?"

Senku hesitated. The question was simple, wasn't it? But the answer was anything but. Something was swirling under his skin. He crossed the room and stopped right beside the bed.

"Gen." he started, voice low "Do you... want to..." His words trailed off, cheeks flushing red. Damn it! He was supposed to be able to handle this like an adult scientist and not a stammering freshman. For half a heartbeat he even considered bolting back to his room, but the hopeful light in Gen’s eyes keep him where he stood.

Gen tilted his head, watching him with curiosity. "Want to what?"

Senku frowned slightly. "You know what."

Gen gave a soft laugh and leaned forward, resting his chin on his hand now. "I do. But I want to hear you say it, Senku."

Senku exhaled sharply. He felt his shoulders tensing. "Do you want to have sex?"

Gen blinked, then smiled. "Do you want to?"

Senku’s stomach flipped. That hadn’t been the question. But now it was, huh? His fists unclenched and clenched again by his hips. "I... I’m not sure?"

Gen’s smile softened as he sat up, his bare feet brushing the floor. "Senku. We’ve been together for a while now. But that doesn’t mean I would expect anything you’re not ready for." He reached out, squeezing Senku’s wrist, a solid  promise that there was no ticking clock. "I just want you to know the door’s open, if you’re curious."

Senku shifted, feeling heat going up his neck. His mind was a mess of thoughts and feelings right now, all tangled together. Wanting, nervous, curious... and unsure what came next.

Gears and circuits I totally get, he thought, but whatever this is... runs on something else.

He let out a shaky breath, moving closer. "I don’t... really know where to start."

Gen patted the mattress beside him, the gesture meant to be casual but kind. "Why don’t we sit together and talk about it first? No pressure."

Senku sat, feeling the bed dip under his weight. His knee brushed Gen’s and tiny sparks climbed up his thigh, sharper than he anticipated. Gen leaned in just enough that Senku could smell the faint fragance of his shampoo.

"Tell me what you’re thinking." Gen murmured.

Senku’s voice was low, hesitant. "I know how things work. I just... I don’t know if I want to. Or if I’ll be good at it. Or if..." He trailed off, looking away.

Gen touched his arm gently. "Hey. Look at me."

Senku met his eyes, heart hammering.

"This isn’t about performance." Gen said quietly. "It’s about what we both want. Together."

Senku swallowed hard. "...Okay."

Gen smiled softly, drawing him into a slow, careful kiss that was more reassurance than heat. Senku’s hands twitched at his sides, then, hesitantly, lifted to touch Gen’s shoulders.

"We can go slow.“ Gen murmured against his lips. "You set the pace."

Senku exhaled shakily. "Okay. I want to try. But... I might need to stop. Or pause. Or…"

Gen nodded, shifting so their knees bumped. He didn’t speak right away. Instead, he studied Senku’s face, reading the tension there.

He reached out, touching Senku’s arm with care. "You don’t have to find the right words right now. You obviously struggle with this. I think a color system could help us. Green means everything feels good and we keep going, yellow is a signal to slow down, pause or check in and red is an immediate stop, always, no questions asked."

He searched Senku’s face. "They might take some of the pressure off. You don’t need to explain everything in the moment, you just check in. That’s all it has to be." he said, voice warm but earnest.

"Just for interest, have you ever used any kind of safeword system before?"

Senku shook his head, cheeks blushing darker. "N‑no. Never really... needed to."

"That’s fine.“ Gen assured him, thumb brushing the inside of Senku’s wrist. "It’s straightforward, but it keeps us both safe. You can say the color, or if talking’s hard just tap my arm three times, whatever feels easiest in the moment."

Senku turned the idea over like a puzzle component, tension easing fractionally.

"That... actually helps.“ he admitted, voice small but sincere. "Structured feedback loop."

"Correct.“ Gen murmured, smiling. "Green to go, yellow to slow, red to stop. And we both promise to listen the first time, every time."

Senku gave a small, nervous laugh. "It’s like an experiment."

Gen grinned. "Exactly. But one where the most important variable is you." Gen leaned forward, brushing a light kiss to Senku’s cheek. "And you have to tell me if something feels off. Promise?"

“Promise.”

★☆★

Senku cleared his throat, heat blooming across his ears. “O‑okay, so... maybe I should... lead? Just at first.”

He wasn’t sure why the words left his mouth. Maybe it was out of instinct, maybe even fear, but there was something about setting the pace that made the moment feel less likely to spiral out of control. Somewhere deep inside, where he couldn’t yet name it, the idea of leading gave him something he could hold onto.

Gen’s brows arched, delighted but respectful. “Captain’s seat is yours, genius. Tell me what you need.”

He lay back against the headboard in open invitation. Senku shifted onto his knees on the bed, suddenly hyper‑aware of every creak of the mattress.

He kissed Gen. One short, searching peck.

Then another.

And a third.

Damn, I don’t know what I’m doing here, Senku thought in a rush, chest tight.

Is this right? Does he like that?

Before he could lose his nerve, he leaned in again and kissed Gen’s neck, slow and unsure, the contact feather-light on the exposed skin. A shiver passed between them. Encouraged by the warmth in Gen’s reaction he pressed another to Gen’s cheek. Then, after a short hesitation, to the curve of his ear.

Am I doing too little? Too much?

A tremble started in his hands.

I just want to get it right... I want this to mean something, not mess it up. 

Panic fluttered at the edge of his ribcage. Senku tried to focus on the moment, but his mind kept racing.

What now? Where do I put my hands?

His hands hovered awkwardly before settling on Gen’s shoulders, fingers trembling.

Calm down already.

Okay.

What’s the next step? 

His hands hesitated, his chest tightening with doubt.

...What if I mess this up? Am I messing this up already?

...

Shit. 

Why are my thumbs so sweaty? he thought in a rush, heart racing.

Senku shifted forward, sliding one hand from Gen’s shoulder to rest on his hip and kissed him again. Tension drew his shoulders tight. Gen caught the faint tremor in Senku’s fingers as his fingertips traced a distracted path over the fabric at his hip. “Yellow?” he prompted gently.

Senku swallowed. “Yellow-ish...?” he muttered. “I was sure I could handle more. I tried to stay in control, but you caught the moment I lost it. I keep over‑thinking. I mean, I know the theory, but right now it seems like my body isn’t listening to my brain...”

“That’s okay Let me listen for both of us.” Gen soothed. “Would it help if I guide us for a while?”

Senku sighed, relieved. Inside, a swirl of tension he hadn’t fully realized loosened. Gen’s offer to guide felt like a hand pulling him back from the edge.

“Would you?” he whispered.

“Of course.” Gen answered, cupping his cheek. “Just breathe and let me look after you.”

Senku nodded gratefully. Gen’s hands slid gently over his sides, easing him down onto the mattress and switching their positions with an easy roll of hips.

“Thank you.” Senku breathed, sinking into the sheets, the pace now firmly, tenderly in Gen’s care.

Gen noticed the tremor still lingering in Senku’s hands. He whispered, calm and soothing. “Hey. We’re not building rockets here, you know? If your hands shake, let them. I’m not leaving.”

Gen leaned in slowly, a gentle smile was on his lips as he closed the space between them. The kiss was soft, slower than Senku expected in this situation. He felt Gen’s hair brushing against his face and the warm touch of Gen’s palm over his side. Every so often, he would pull back just enough to press a kiss to Senku’s cheek. Or at the curve of his neck. Or simply to cup his face in both hands and rest their foreheads together. He ran his fingers through Senku’s hair with awe, thumb brushing the line of his jaw.

It wasn’t about seduction, it was comfort, grounding, a quiet I’m here. And with every touch, Senku felt his breath slow, his pulse begin to settle. It made it easier to stay present.

Gen pulled back slightly, smiling. "Hey." he murmured, brushing Senku’s hair back. "We’re in no rush." Senku flushed scarlet. A warm prickle swept over his skin, feeling as if every point of contact had been loaded with static.

He swallowed hard and nodded. "R‑right. I know." His voice cracked anyway.

They kissed again and again, until Senku felt himself begin to sink into the rhythm. His muscles loosed, his heart pounded a little less painfully. Gen kissed along his jaw, then paused to snuggle behind his ear, breathing a soft sigh that tickled Senku’s skin. His fingers traced lazy lines over Senku’s chest and across his stomach. His fingers slid up over the fabric of Senku’s shirt, nudging it higher with each gentle brush. Then he hooked his thumbs gently under the fabric at Senku’s sides, a silent question in the motion as he began to guide the shirt upward. It wasn’t wrong, but paired with the heat of Gen’s mouth on his neck and the growing weight of sensation, it sent a jolt of nerves through Senku’s system, a too-much-too-soon he hadn’t anticipated.

"Yellow.“ he said, barely more than breath.

It wasn’t one thing. It was all of it. The closeness, the pressure, the not knowing what came next.

Gen froze instantly, pulling back just a bit, one hand stroking softly down Senku’s arm. "Okay. You’re doing great. Want to tell me what’s going on?"

Senku squeezed his eyes shut, cheeks flaming. "I just... I don’t know. It’s a lot."

Gen kissed the side of his head gently. "That’s okay.” he soothed. "We can stay right here and slow everything down. Tell me what feels best, do you want me to keep going at this pace, or do we take a short pause?"

Senku hesitated, his pride sparking but then his shoulders sagged. "Short pause.“ he whispered. "Please."

Gen’s hand slid lightly down his arm, grounding him. He noticed the subtle shiver still lingering in Senku’s hands and drew back slightly, letting the kiss fade rather than finish abruptly. "Breathe." Gen whispered "It’s okay."

God, how does he do this? How does he know exactly when I start to spiral ?

Senku let out a sharp exhale, realizing how tense his shoulders were once again. He took a few deep breaths, steady and intentional, until his shoulders began to relax under Gen’s quiet presence.

"Okay. Recalibrated. We can continue." he murmured, voice tight. "Sorry."

"Nothing to be sorry for." Gen kissed the corner of his mouth. It was warm and coaxing. He kept the touch light, more as a reassurance than an invitation, giving Senku space to lean in or stay still. His fingertips skimmed under the hem of Senku’s shirt again, resting lightly against his skin, waiting. Not pushing.

Just a question.

Senku’s breath hitched. Uneasiness tightened his chest again. "Green.“ he whispered, almost before he could second‑guess himself.

Gen smiled softly. "Good." He eased Senku’s shirt up, watching his face, making sure each movement was met with a nod or a quiet, whispered confirmation. When the shirt finally came off his face, Gen dropped it onto the floor like a stage prop, getting a quiet, uneven laugh from the blushing scientist.

Senku’s chest felt tight. Not from discomfort, but from the sheer unfamiliar vulnerability of it all. His heart raced, thundering in his ears. But every time he started to spiral, Gen’s soft murmur or grounding touches pulled him back.

They kissed again, deeper now, but still slow. Gen’s weight shifted slightly, pressing Senku back onto the bed, their legs tangling. Senku gripped Gen’s shoulders, squeezing his eyes shut for a moment, overwhelmed by the sensation, the closeness, the heat curling low in his stomach.

Gen paused. "Color?"

Senku opened his eyes, cheeks blushed. "...Yellow. Just... slow down a second."

Immediately Gen’s hands stilled, his body easing back just enough to let Senku breathe. He kissed Senku’s temple, the gentlest press of lips. "You’re doing great.“ he murmured. "Just tell me what you need." Keeping the pace unhurried, he shifted his weight back long enough to peel his own T‑shirt over his head and toss it to the floor, giving Senku a moment to settle while the sudden warmth of bare skin replaced the cotton between them.

Senku let out a shaky breath. Then another. Slowly, his fingers uncurled from the sheets, his eyes lingering on the soft, exposed line of Gen’s chest. For a heartbeat he could only stare, wonder and nerves tangling together beneath his ribs. Gen caught Senku’s wide‑eyed stare and offered a gentle half‑smile. “All good. Check me out as long as you need.”

Senku startled, heat blooming across his cheeks. “T‑tch. If staring is a crime, arrest me later. Right now I’m... processing. A lot.”

He drew a breath, cheeks still burning, and muttered, “Okay. Go ahead.”

Gen smiled, brushing his nose lightly against Senku’s before continuing, this time with his hand trailing down Senku’s side, feather‑light. Gen paused at the button of Senku’s pants, waiting patiently as Senku took a slow breath, steadying himself. After a few seconds, Senku nodded softly, a quiet, resolute permission. Gen  worked open the button of Senku’s pants, watching for any flicker of hesitation, every shift of breath. When his hand slipped inside, it stayed above the boxers, cupping gently through the soft fabric. Senku gasped softly, hips jerking and for a split second, panic flashed in his eyes.

"Color?" Gen murmured immediately, his voice a low, grounding note.

Senku gulped air, redness creeping up his face. "Yellow." His voice was thin, but steady. "Just... just a moment."

Gen kissed his forehead, murmuring reassurances, gently withdrawing his hand from Senku’s pants before letting his fingers stroke slow, soothing patterns along Senku’s hip instead of pushing further. "You’re allowed to take all the time you want."

Senku’s chest tightened, not with anxiety this time, but with a deep, almost aching gratitude. He hadn't realized trust could feel this physical, like an extra heartbeat growing in his ribs.

He’s not rushing me.

He’s not expecting anything.

He’s just... here.

Slowly, breath by breath, he let the tension inside him ease. His hand drifted to Gen’s arm, fingers squeezing gently. "...Okay.“ he whispered. "Green."

Gen kissed him softly. His hands were warm, his touch feather-light, coaxing rather than urging. At first his palm stayed through the thin fabric of his boxers again, the pressure light and steady, sending sparks through Senku’s stomach. Gen didn’t move too quickly. He waited, fingers still, until he felt Senku’s hips shift, just slightly. An unconscious lean into his touch. It was enough. He let his hand slip beneath the boxers, gentle and controlled. Skin meeting skin, warm fingers wrapping slowly around his cock. The sudden intimacy made Senku gasp, hips jolting with a mix of pleasure and raw vulnerability. For a heartbeat, panic prickled again, but the grounding pressure of Gens free hand on Senku’s bare stomach kept him steady.

As Gen began to stroke him, slow and rhythmic, the skin-on-skin contact pushed Senku’s senses into overdrive. His mind spun, breathing stumbled, thighs tensing, and suddenly he blurted "...Yellow!"

Gen’s hands stilled instantly, and he gently slid the one that had been tucked inside Senku’s trousers back out, letting his palm settle on Senku’s hip in a steady, grounding touch. "Good, Senku. That’s good.“ he soothed, voice low and reassuring. "You’re in charge. We go at your pace. No matter what."

Senku pressed a shaky hand over his eyes, chest heaving.

T his is okay.

He’s still here.

Not annoyed.

It’s safe.

Slowly, his breathing steadied again.

Minutes stretched, quiet except for their breaths and the occasional whispered check‑in. When Senku felt the trembling ease slightly from his chest, he whispered "...Green."

Gen kissed his temple, his hair, his cheek, a trail of soft warmth leading back to his lips. "Thank you.“ he murmured. "Thank you for trusting me."

Senku’s throat felt thick. He pressed his face into Gen’s shoulder, letting the closeness steady him.

Dad was right. This isn’t just sex. It’s trust, it’s choosing each other, it’s... something I never thought I’d need.

Gen’s hand returned to its slow exploration, sliding down Senku’s stomach until his knuckles brushed the waistband of those still‑in‑place trousers. He paused there, rubbing soft circles over the cloth‑covered bump of arousal, neither rushing nor retreating.

“Color?” he asked, voice a warm murmur against the shell of Senku’s ear.

Senku’s breath hitched, hips giving a tiny, involuntary jerk. “Still green.” he whispered, surprised by the steadiness that came with saying it aloud.

“Good.” Gen praised, teasing a faint line with the pad of his thumb from base to tip through the fabric. The friction made Senku gasp, heat rushed up his spine. Gen kept the touch light, almost honoring, until the tension in Senku’s thighs shifted from anxious to eager.

When Senku’s fingers finally sank into Gen’s hair, tugging just enough to say more, Gen looked up and met his eyes. “Ready to lose this last layer, genius?”

A rosy flush crept across Senku’s cheeks, but his nod was sure. “Green.” He added, a wry ghost of a smile twitching at his lips, “For science.”

Gen chuckled softly, pressing a brief, grateful kiss to Senku’s hipbone. “For us.” He slipped his fingers beneath the waistband, giving Senku plenty of time to change his mind. No color came. Senku lifted his hips in permission.

He eased the waistband down in one unhurried motion, pausing each time Senku’s breath caught and only drew trousers and boxers away when that shaky inhale eased out into a breathy nod.

Senku’s hips settled back onto the sheets, the cool air ghosting over newly bared skin. For a heartbeat he could only stare wide‑eyed at the ceiling, pulse roaring in his ears, aware in a way he had never been of the weight and warmth of his own body.

Gen's hand, now free, settled on Senku’s thigh, thumb brushing slow circles again. His pupils were blown wide, mouth parted in soft admiration.

“Genius.” he murmured, voice low-key awed. “You are, scientifically speaking, gorgeous.” He eased back just enough to take in the view he’d just revealed.

Senku’s cheeks flared hot, but the compliment burst in his chest like a small firework. He swallowed, eyes darting anywhere but Gen’s. “Y-you don’t have to... analyse it.”

Gen chuckled, warm but earnest, thumb brushing over the sharp line of Senku’s hip. “May I touch you again?”

Senku drew a breath that trembled at the edges, then gave one short, decisive nod. “Yes. Green.”

Gen’s fingers wrapped gently, almost reverently, around Senku’s cock. The contact was firmer than before, skin‑to‑skin, slicked only by the faint sweat that had gathered in the warm confines of his underwear. Senku’s head tipped back, a startled sound catching in his throat. The sensation was impossibly bright, every slow stroke seemed to pull a wire of tension tighter from his belly to his lungs.

“Color?” Gen whispered after three strokes, squeezing just enough to make Senku gasp.

"G‑green.“ Senku breathed, though the word twitched on the edge of a moan. One hand fumbled up to grasp at Gen’s forearm, not to stop him but to anchor himself. Gen kept the pace unhurried. Long pulls that let Senku feel the glide from base to tip, the faint twist of a wrist that made his toes curl.

Senku’s chest rose and fell in uneven bursts, a fine layer of sweat shimmered at his collarbones.

So this is what everyone keeps talking about, his scientific mind provided uselessly, before short‑circuiting beneath another careful squeeze. Heat settled low, muscles tightening, pleasure drifting the fine line between exhilarating and overwhelming.

After several minutes Senku’s thighs began to tremble, his breath stuttering. A flash of panic flickered, too fast, too much... he gasped, “Y‑yellow.”

Instantly the rhythm gentled, Gen’s strokes slowing to soothing passes meant more to calm than excite. He leaned over and pressed a kiss just below Senku’s navel. “You’re doing wonderfully. Whatever you need, just say it”

Senku gulped air, chasing scattered thoughts. "Need a second. Gravity shifted sideways." he admitted, voice rough.

“Take all the time you want.” Gen assured him, releasing his grip but keeping his palm resting warm and steady atop Senku’s hipbone. He waited until Senku’s breathing evened, until the restless spark in his eyes settled back into focused awareness.

Senku finally nodded, a faint, fragile smile tugging at his lips. "Green."

Gen continued stroking for another lingering minute, reading each hitch of breath until the tension in Senku’s hips shifted from startled to seeking.

Senku’s mind fluttered between bursts of sensation and a stunned kind of wonder. He had never been this bare, this touched, this exposed in front of someone. It was terrifying and breathtaking all at once. His nerves sparked and vibrated, the anticipation sharpening every breath but it didn’t send him into panic this time. Because Gen was still here, anchoring him, reading him, holding steady. That quiet, deliberate presence calmed the static in his brain, helped his breathing find a rhythm, helped his body begin to believe this is okay. And as the fear ebbed, it left a single, quiet truth in its place. 

Yes, I want this. I want him.

Gen slowed his hand, easing the rhythm to a halt. Senku blinked, a small furrow creasing his brow. “Why did you stop?” There was a flicker of uncertainty in his eyes. Not fear but confusion, like his body and mind had momentarily lost sync. Gen noticed it instantly. He leaned in just a little, brushing his nose lightly against Senku’s. “You looked overwhelmed for a heartbeat. Beautiful, but somewhere else. Wanted to bring you back.”

Senku hesitated. “I just... didn’t expect it to feel like that.”

Gen smiled, soft and steady. “New terrain. You’re allowed to be surprised.”

He traced a finger lightly along Senku’s stomach, eyes full of quiet certainty.

“We can stay right here and I’ll keep touching you until you finish.” he murmured, thumb tracing idle circles along Senku’s inner thigh. “Or, if you want to feel something new, I can take us to the next step. All at your pace, genius. What sounds right?”

Heat flushed up Senku’s neck. The idea of finishing under Gen’s hand was tempting, his body already hummed at the edge, but curiosity tugged harder. “If we stop now I’ll probably melt down.” he admitted with a shaky laugh. “But I don’t just want to rush to the end. I... want to know what the next step feels like. Please talk me through it.”

Gen’s expression turned impossibly gentle. “We can circle back and make you come this way any time.” he promised, pressing a kiss to the inside of Senku’s knee. “But I thought we might explore something different first. Only if you’re interested.”

Senku nodded, breath unsteady but determined. “Green.”

“Alright.” Gen said softly, shifting to reach into the drawer beside the bed for the lube, laying the bottle beside them on the mattress. “Fingers first. Plenty of slick, nice and slow. We’ll start with just one, add more only if you want. Nothing moves forward unless you say green and we can stop or switch back to my hand on your cock whenever you like. Later, if it still feels good, we can talk about me going inside, but that’s entirely up to you.”

Relief loosened something tight in Senku’s chest, the clear roadmap steadied the swirl of nerves. He managed a whispered “Thank you.”

Gen’s answering smile was tender, full of pride. “Thank you for trusting me, genius.” He leaned up to kiss him, slow, sweet, unhurried... before murmuring against his mouth “Ready for this?”

Senku answered with a shaky but certain “Yes.”

Gen reached for the bottle of lube again, clicking it open. The faint, unmistakable scent of clean gel filled the air. Senku’s heart thudded. He felt Gen’s fingers stroke down his thigh, pausing again.

"Color?" Gen asked softly.

Senku drew a shaky breath. "...Green."

Gen warmed the lube between his fingers, pressing soft, careful kisses to Senku’s jaw as he settled between Senku’s parted legs. Senku felt every tiny movement. The shift of weight on the mattress, the slow drag of fingertips along his skin. The first slick fingertip pressed gently and Senku gasped, hips twitching.

"Yellow." Senku managed.

"Okay. We slow down." Gen kissed his knee, his thigh, tracing calming circles. "You’re doing so well, love."

The word love wrapped around Senku like a shockwave. His eyes stung. His chest felt too full.

When he whispered "...Green again" Gen went on, breathtakingly patient. He kept to a single finger at first, press, pause, retreat, letting Senku’s body learn the rhythm without overload. Between those gentle strokes he bent to press slow kisses across the pale plane of Senku’s stomach, murmuring encouragement that warmed him up and made his shoulders unwind.

“Color?” Gen paused after the shallow curl of his finger brushed a spot that made Senku’s breath stuttered.

“G‑green” came the trembling reply, but the hand gripping Gen’s forearm never pushed away. Encouraged Gen continued the same unhurried pattern, spreading fresh lube, never pushing deeper than Senku welcomed.

Eventually he went still, resting his forehead against Senku’s thigh. “Whenever you feel ready for the next step, just tell me.” he whispered.

Senku’s cheeks were burning, eyes bright with sensation he didn’t yet have words for. He focused on the grounding weight of Gen’s palm over his hip, on the measured drag of air into his lungs. After several breaths he licked his lips and whispered “I... think another would be okay.”

Only then did Gen ease a second finger alongside the first, millimeter by millimeter, stopping every few seconds for a color check. Each careful stretch was met with soft encouragement, murmured assurances of how well Senku was doing and how beautiful he looked opening for him.

When he flinched sharply at the new stretch, a tiny noise escaped him. "Y‑yellow."

Gen soothed, waited, kissed his temple. The light trail of kisses along sweat‑damp hair grounded Senku more effectively than any focus technique. Time stretched like honey, slow and golden. Finally Senku nodded, whispering "Green..." and Gen continued.

Gen eased his motions until his two fingers glided without resistance, then stilled, only his free hand smoothing circles over Senku’s thigh.

“Genius, before we go further I’d like to add one more, just to be sure everything feels comfortable. Trust me, it’ll make the next step smoother.” His tone was soft, checking rather than coaxing.

Senku’s breath came in fast, excited puffs, he blinked hazy eyes open. Desire and nerves wrestled in his ribs, but the thought of less sting, more glide, made logical sense. “O‑okay. Green.” he whispered, voice rough but resolute.

Gen kissed the inside of his knee in gratitude, worked more lube between slick fingers, and pressed the pads together, entering with painstaking care. A gasp left Senku, sharp, then melting into a low groan as the stretch settled.

Gen didn’t move until Senku’s fists unclenched from the sheets. “Color?”

“G‑green,” Senku breathed, a flicker of wonder in the word. Gen resumed, slow scissor and shallow curl, teaching muscles to loosen.

When the burn dulled to heat and the heat to a curious fullness, Senku’s hips began to rock, small but deliberate. His eyes fluttered open, cheeks blazing.

“I’m...ready for this. Please.” he murmured, almost shyly.

As Senku steadied his breathing after the third finger, Gen sat back to tug off his pants, moving unhurriedly. Senku watched, heat blooming in his cheeks but saying nothing. It was the first time he’d seen Gen completely bare, every line and curve of his body exposed in the dim light, cock hanging flushed and thick between his thighs. The sight struck Senku breathless. Arousal flared low in his belly, sharp and unbidden, just from looking.

Gen caught the look and smiled as he reached over his shoulder to the backpack at the foot of the bed. He rummaged only a moment before producing a condom, one of two he’d had stashed in his backpack for months, just in case.

Senku had never actually seen the motion up close. Gen pinched the tip, rolling latex downward in one smooth stroke. The glide of slick, the little gasp Gen gave at the first contact, stirred something new and electric inside Senku.

It’s strange seeing this step in person, not in diagrams or biology books... strange, but oddly comforting.

This is real.

We’re real.

Gen brushed sweat‑damp hair from Senku’s brow, pride shining. “If anything feels off, just say the word. I'll stop right away.”

Eventually, edged with trembling, Senku whispered, "Okay... try."

The moment Gen began to push inside, Senku’s world narrowed. Nothing existed but the slow stretch, the heat, the impossibly intimate pressure of another person entering him. Gen inched forward, barely a centimeter at a time.

It was unfamiliar, intense, like his body had been rewired. Not really pain, not even discomfort, just... too much to name.

He breathed. In, out. Let his fingers find Gen’s back and settle there, needing the anchor.

Halfway inside, Gen’s breath stuttered, a soft, ragged sound of pleasure he couldn’t completely hide.

“That good?” Senku managed, voice shaky but curious.

“God, yes.” Gen murmured, pressing a kiss to Senku’s brow. “You feel... incredible. But we don’t move until you’re ready.”

Gen stopped once fully inside, holding perfectly still, his breath ghosting against Senku’s cheek.

And in that stillness, Senku felt it. This was the step. The feeling he hadn’t known he’d longed for. The sense of being filled, not just physically, but seen. Wanted.

His palms pressed lightly between Gen’s shoulder blades. A silent yes.

They stayed like that for long seconds while Senku’s muscles adjusted, a faint burn softening into deep pressure, then a pulse of surprising pleasure spreading low in his belly. He flexed experimentally, feeling Gen stifle a groan above him.

"Color?” Gen asked again, voice rough-edged now.

“Still green.” Senku said, a tentative spark of pride flickering behind the words.

Gen drew back slightly, rocked forward again, gentle, deliberate. The motion rubbed over something that made Senku’s back arch. Heat bloomed, he gasped, nails digging into Gen’s shoulders.

“That?” Gen whispered, mouth brushing Senku’s ear. “Good?”

“Y-yeah. It’s... hah... it’s good, just a lot.”

Gen set a slow rhythm, tiny thrusts, more pressure than speed, while watching every flicker across Senku’s face. After a dozen breaths Senku’s thighs quivered, the fullness turning overwhelming, a pressured wave of emotion tightened his chest.

Panic flickered. The pleasure was too bright, too sharp. It hit him like a jolt, unfamiliar and unmanageable. For a moment, Senku felt the delicate illusion of control slip, his body responding faster than his brain could keep up, every nerve sparking without clear instruction. His breath stuttered. “Red!” he croaked, almost surprised by his own voice.

Instant withdrawal. Gen eased out and gathered Senku close before the word even finished, peppering his temples with kisses. “Okay, okay, we stop. You did amazing.” He tucked Senku firmly into his arms, one hand combing through sweat-damp hair, anchoring him while the rush ebbed.

For several heartbeats they lay quietly, neither speaking. Senku’s breath gradually slowed, his tense muscles loosening one by one. The quiet between them wasn’t strained. It felt like a necessary pause, a gentle return to safety and balance before either could think about talking again.

Senku trembled, face hidden, breaths ragged. He wasn’t hurt, just overwhelmed, cracked wide with feeling.

It’s okay. I’m not weak for needing to stop. It’s safe. He promised, and he meant it.

Gen whispered, "I’ve got you. Thank you for telling me. Thank you for trusting me."

It felt like centuries before Senku could speak. "Th‑thank you.“ he rasped. "It was... a lot. But I- I’m okay."

Gen kissed his hair. "Let me clean us up. Then I’m not letting you out of my arms." Gen tugged the condom off, knotted it and tossed it in the trash.  He fetched a warm cloth from his bathroom, wiping them both gently, tucking the blankets up.

★☆★

They lay curled together in the dim light, legs tangled, Senku’s head pillowed on Gen’s chest. Gen’s fingers traced lazy circles over Senku’s shoulder blades.

Senku spoke first, voice small. "I thought I wasn’t interested in sex at all. Tonight I realized... I’m interested in feeling safe with you."

Gen’s chest hitched. "Hmmm. I used to think sex was just... something you endured to feel wanted. But this? With you? It wasn’t the act that mattered. It was the trust."

He hesitated, fingers still absently tracing circles over Senku’s side, before adding even more quietly “And... I’m not really used to being the one topping, either. With Hyoga I was always the one taking. Never asked, never guided, it just... happened.”

Gen swallowed, meeting Senku’s gaze. “So tonight I wanted everything to be about your comfort. Every pause, every color check... I needed you to know this was ours to shape, not something you had to endure."

Senku let out a breathy laugh. "A few weeks ago I was the one grounding you. Now you’re grounding me."

"That’s synergy, genius." Gen pressed a playful kiss to his forehead. "We balance the equation."

Senku flushed but smiled. "Nerd."

"Takes one to love one." Gen’s fingertips brushed Senku’s cheek. "How’s your breathing?"

"Steady now. Chest still feels... full."

"Full‑good or full‑bad?"

"Full‑good. Like... like I I unlocked a surprise data trove."

"We can analyse it tomorrow."

Senku chuckled weakly. "I already have a theory that cuddling you reduces anxiety by ninety‑three percent."

"Peer review says confirmed." Gen tightened his arms around him, the blankets rustling softly.

Senku let his gaze drift. Gen looked... messy. Flushed. Hair sticking up from sweat and kisses. Beautiful, in a way Senku didn’t have the vocabulary for.
He wasn’t sure he’d ever be good at saying these things out loud. But maybe, just maybe, he could learn.

For the next while they stayed exactly as they were, warm skin against warm skin, the blanket cocooned around them while their pulses slowed bit by bit. The steady slide of Gen's palm over Senku's ribcage was a metronome, and for several long minutes neither of them wanted to shift even a centimeter. Eventually though, the night air sneaked beneath the blanket and a subtle shiver chased across Senku's shoulders.

"Getting chilly?" Gen whispered.

"A little." Senku sounded almost embarrassed to admit it, the closeness felt too perfect to break. Gen solved the problem by kissing his temple and slipping from the bed just long enough to fetch two bottles of water and rummage in the bottom drawer. Senku remained under the blanket, skin still humming from every new sensation, eyes tracking Gen's silhouette in the low light.

When Gen returned he handed over the water first, then pressed a soft bundle into Senku's hands. One of his own oversized hoodies and a pair of loose lounge‑pants. "Only until you warm up again.“ he murmured. "And yes, you can keep the hoodie hostage as long as you like."

Senku pulled the pants on under the covers, then wriggled into the hoodie. It fell to mid‑thigh and smelled faintly of citrus shampoo and Gen's cologne. The fabric was ridiculously soft, the borrowed scent grounding in an entirely new way. Gen slipped back beneath the blanket, gathering him close so that their legs still tangled, bare skin still touching along their calves.

"Better?"

"Yeah.“ Senku admitted, nuzzling into the collar that overwhelmed him in plush cotton and Gen‑smell. "Still counts as skin‑to‑skin contact somehow." The joking tone in his voice was small but genuine, proof the anxiety had ebbed.

Gen chuckled, pressing his lips to the edge of the oversized hood. "Evidence that thermodynamics and affection go hand in hand I guess." He tucked Senku closer against his chest, winding his arms tighter so their warmth radiated between them. Senku lay perfectly still for several long moments, letting the quiet comfort settle over him before he finally exhaled.

Gen felt the subtle change in Senku’s breathing, a notch too quick, as though new gears were spinning in his head again. He pulled back just enough to study Senku’s face. "Thought spiral?"

Senku huffed into the hoodie fabric. "Just... forecasting." He drew a shaky circle on Gen’s chest with one fingertip. "I want to do this again. Sometime. Being that close, feeling you... it flipped a switch I didn’t know I had. But I’m still processing the results. Might take a while before I’m... ready-ready. And next time I want to give something back, not just be the one receiving."

Gen’s thumb brushed the shell of Senku’s ear. "You already gave me something, genius. That trust? Hearing you say you want more with me? Better than any orgasm I’ve ever had."

Senku let out a tired laugh. "You’re getting sentimental on me, huh?"

"Maybe. Doesn’t mean I’m wrong." Gen kissed the crown of his hair. "Whenever you’re ready, in whatever form, I’ll be right here. Eager lab assistant at your service."

Senku’s answering chuckle was soft, but the tension eased out of his shoulders. "One step at a time... I’ll know when I’m ready for the next. I let you know." He burrowed closer, letting the warmth settle in his bones.

Gen watched him until his own eyes slid shut. Wary guardian, proud lover.

"But uhmm... Gen?"

"Mm?" Gen hums softly, fingers threading idly through Senku’s hair.

Senku hesitated, then said, voice barely above a whisper, “Remember... in Houston  when you mentioned sharing a shower? Tomorrow... maybe we could do that together?”

Gen blinked, then smiled so gently it hurt. “Yeah? You’re sure?”

Senku flushed. “I was too overwhelmed when you suggested it. I couldn’t do it then. But now... I think I want to. Just being near you like that, without pressure.”

Gen pressed a kiss to his forehead. “Of course. I’d love to.”

Senku, nestled comfortably against Gen, suddenly lifts his head slightly, eyes sleepy but intent.

Before sleep claimed them, Senku mumbled, half‑dreaming, voice scratchy but certain, "Love you." Even as his eyes drifted shut, a small pulse of amazement stirred in his chest. How strange and wonderful it was to say those words and feel them reflected back.

Gen’s answering whisper was the last thing either of them heard: "Love you too, genius. Sleep."