Archive of Our Own ^beta

Chapter Text

“Ack!” you hissed, snapping your wrist after another sharp jolt. You’d stopped counting how many times the static had zapped you. Dust clung to your skin until you felt like the nucleus of a plasma globe.

Senku had dumped you in the village laboratory with yet another mind-numbingly tedious task—grinding down sulfur, charcoal, and a handful of other gray minerals into fine powder.

The generator humming threateningly nearby didn’t help.

“‘Even a baby could do it’ ? Go to hell,” you muttered, rolling up your sleeves. You pressed the pestle back into the mortar, each grind more grudging than the last, the rasp of stone on stone matching the irritation buzzing in your veins.

Your hand swept across the cluttered tabletop of the lab, grasping at empty air where the mineral should have been. You turned, scanning the jars and trays again, but it was gone. A resigned sigh pushed through your teeth as you stood to check properly.

Still missing. Which meant another trip to the storehouse.

You headed for the door, only to catch one last static snap from the generator on your way out.

“Ugh—damn it!” you spat, shaking out your hand. 

The chill of night hit you the moment you stepped outside.

You slipped into the storehouse, greeted only by the faint creak of the door. 

“Seems like Chrome is sleeping in the village again,” you murmured, noticing his absence. Night duty was yours alone. Sometimes Kinro nodded by at the bridge before dawn if he happened to wake early, but after yesterday’s brutal training, even he was out cold.

Being a night owl in the old world had meant dragging yourself through mornings half-dead, teachers side-eyeing you for yawning through class. Here, it was a different story. No one minded if you stayed awake under the moon. No one except Senku, who only called you “lucky” for not getting grilled with questions like some all-knowing oracle of science.

You moved down the rows of glass containers, eyes flicking over their dull shapes. The mineral you needed had to be here somewhere.

…Wait. Which mineral was it again? They all looked exactly the same.

You groaned, dust clinging to your sleeves, fingers hovering uselessly over the jars. The static prickled your arms again, making you flinch.

Your eyes drifted to the wooden roof above, the little door where Senku usually slept. A part of you thought about trying to sort them yourself—but then his voice floated back, dry and smug:

“Seriously, even a baby could do this. Just sort by size or color. Basic observational skills, Graveyard Shift.”

You muttered under your breath, “Yeah, thanks, genius,” and shook your head. Picking up two sample minerals, you squinted, turned them, tapped them together, and still couldn’t see a difference.

Clearly, Senku had overestimated your ability to tell these rocks apart.

Sighing, you climbed up the step ladder to the observatory. Looks like it was time to wake Senku. Hopefully he’d be less annoyed than he would be tomorrow when faced with half the powder he expected.

You heaved the door over your head, muscles tense as the hinges groaned. 

“Wake up, you damn…” Your words caught in your throat as your eyes fell on the scene inside.

The moonlight fell across him, highlighting the sheen of sweat on his skin. Loose cloth clung unevenly, shifting with every sharp breath he drew. His chest rose and fell rapidly, the rhythm erratic, the quiet panting filling the room. 

White drops glimmered on the floor near him, and your gaze darted to his hand, in motion. Startled, you lost your grip on the trap door. It swung down sharply, smacking the back of your head with a painful thud.

Senku’s eyes widened the instant he noticed your gaze, embarrassment flaring across his features. A flush spread rapidly from his neck to his cheeks, sweat glistening even more under the moonlight. His lips parted as if to speak, then snapped shut, and his hand froze mid-motion.

And that was the day your gruelling tasks were increased threefold. 

———

It had been a week since… that incident. And ever since, Senku had been cold to you, acting like it was somehow your fault.

Maybe it made sense, in a twisted way. You’d be mortified too if someone walked in on you flicking the bean—your most private, ridiculous moments exposed for some person to see. 

But, c’mon. You had definitely paid the price.

You had been unfairly tasked with heavy-duty work all morning, hauling heavy sacks that left your arms trembling. Hours had passed, and by the time the sun climbed higher in the sky, it was nearly noon—your sacred, dozing time. Your body ached, and every nerve felt frayed.

Kohaku had noticed your sluggish gait and waved you over to the river. “Come on, take a break. You look like you’re about to collapse,” she said with a small smile.

Now, sitting on the smooth rocks at the water’s edge, you gazed into the river, watching sunlight scatter across the surface. The gentle lapping of water seemed to pull some of the tension from your shoulders. For a few moments, neither of you spoke.

Then Kohaku broke the silence, her voice soft but curious. “What’s eating you?”

You hesitated, cheeks warming. “…So, hypothetically,” you began, stumbling over your words, “what would you do if you… maybe, hypothetically, of course, saw someone kind of naked?” 

You carefully left out the part that you saw Senku giving Lil’ Senku a workout.

Kohaku blinked at you, calm as ever. “It’s natural. Happens all the time.”

You groaned, whining. “No, it’s not!”

She leaned closer and playfully nudged your shoulder with hers. “We’re both naked right now.”

You froze. “…Yeah, but it’s different. We’re both girls.”

Kohaku’s expression was amused, matter-of-fact. “Even if we weren’t… wouldn’t it still be ordinary?”

Your gaze dropped to the water, your thoughts spinning. Of course—her era wasn’t as modest as yours. Accidents like this didn’t carry the same weight for her. 

You flopped back against the smooth rock, tugging at your wet hair. Kohaku’s calm gaze never wavered. “Look,” she said, finally, “if it bothers you this much, there’s only so much you can do. You’ve got to… deal with it.”

“Deal with it?” you repeated, incredulous. “How? By pretending it didn’t happen?”

She shrugged lightly. “Exactly. Move on, live your life.”

You chewed your lip. “I think… I’m more worried that he’s more embarrassed than I am.” Your voice dropped, almost a whisper. “Like I walked in on something private, and now he hates me or is angry at me…”

Kohaku gave a soft sigh, shaking her head. “You’re overthinking it. Seriously. Most of the time, people are too busy to dwell on what you saw. But…” She leaned back slightly, her tone gentler, “if it would calm your mind, maybe a simple apology would help. Just… acknowledge it without making a big deal. That’s it.”

You stared at the water, splashing lightly at the surface. Apologize. Keep it small.

Kohaku leaned back, letting out a quiet sigh. “Honestly, it’s really not that big of a deal.”

Just then, a chirpy, overly enthusiastic voice carried from the distance. “Ya-Ho! Mind if I join in?”

Without missing a beat, Kohaku spun around, eyes blazing, and shook her fist in the air. “Gen. You perverted, sleazy man!” she shouted, her voice echoing across the river. “Not another step!”

Gen’s voice carried from the distance, muffled but dramatic. “Kohaku-chan… so cruel!” you heard him cry as he slinked away, still whining about being chased off.

You couldn’t help a small, amused smile despite yourself. Turning to Kohaku, you said softly, “Thanks… for the advice.”

She shrugged, brushing water from her hair. “Don’t overthink it. Just… be honest, keep it simple.”

“I will,” you promised, taking a deep breath. “I should go apologize.”

You slipped out of the river, the cool water leaving goosebumps across your skin. After quickly getting dressed, you made your way to the lab.

The room was quiet, the afternoon sun spilling across the countertops. Senku was there alone, tinkering with some apparatus, his usual focused expression in place.

You stepped inside cautiously. He glanced up from his work. “What do you want?”

You shuffled your feet, suddenly aware of how stiff your arms and shoulders felt. Words caught in your throat, and instead of blurting out that you were there to apologize, you asked nervously, “Uh… what are you doing?”

Senku didn’t look up immediately, carefully adjusting a tiny component. “I’m building a headlamp,” he replied, his tone casual but precise.

“Oh… a headlamp?” you repeated, voice a little higher than usual. “What’s it for?”

His eyes flicked to you, sharp and calculating. “Headlamp. Lamp for the head. If you had all that time for stupid questions, you’d have plenty of time to finish another chore,” he said, already returning to his tinkering.

You groaned, realizing your attempt to ease the tension had backfired. “I—uh—I’m sorry.”

For the first time, Senku set his gadget down and finally gave you his attention. “You still haven’t learned to knock on the door.”

You froze, then turned around. “…Right. I didn’t knock.”

“That’s what I said,” he said flatly.

“It was… last time it was a trap door, not an actual door,” you mumbled.

Senku scoffed. “There’s door in the name. That should’ve been enough.”

You felt heat rush to your cheeks. “…I know, I know…” you muttered under your breath, glancing down at the floor. Your fingers twisted nervously. After a long pause, you tried again. “…It’s… it’s normal. You were… jerking off. It’s not… that embarrassing.”

His eyes narrowed, sharp and calculating, making your stomach twist. “This is about your lack of manners. Why are you blaming me?”

You shook your head quickly, stumbling over your words. “I’m not blaming you! I get it… I mean… sometimes even I get horny too, you know?”

Senku looked up, one eyebrow raised. “Don’t compare your… primitive urges to my quick stress relief method. Totally different systems at work.”

You blinked, tilting your head. “…Aren’t they practically the same thing, though?”

He sighed, as if he couldn’t believe you needed this explained. “No. I’m doing it for efficiency. You’re doing it for pleasure. That’s the fundamental difference.”

You chewed your lip, cheeks warming, trying to figure out how to say it. “…But doesn’t it come down to the same thing, in the end? Both of us just… trying to feel better?”

Senku gave you a flat look. “No. I’m cutting down tension so I can keep my brain running at full capacity. You’re chasing dopamine for the fun of it. Two entirely different categories.”

Your mouth twisted. “Okay, fine, Mr. Science. Stress relief, mental clarity, whatever you want to call it. But it’s still your body. It’s not like you can separate it from… y’know.”

He exhaled through his nose, sharp and impatient. “You’re circling back to pointless semantics.”

Well… you’d already dug yourself a hole. There was no turning back now. Every blush, every fumbled word from earlier made the idea of saying anything even more terrifying—but staying silent wasn’t helping either.

“Maybe,” you muttered, eyes dropping to the floor. “But… I keep thinking there has to be a way for both of us to get what we want without… all this awkwardness.”

That made him pause, crimson eyes narrowing slightly. “…Both of us?”

You nodded, throat tight. “Yeah. You don’t want anyone barging in again, and I…” You hesitated, heat crawling up your neck. “I wouldn’t mind if… I got something out of it too.”

His stare sharpened, voice low. “What exactly are you proposing?”

Your pulse spiked, but you forced the words out. “Well… you could… provide me, uh, dopamine whatever while I… help with your stress relief in return.” A beat passed before you blurted, “So… sex.”

Senku’s eyes narrowed, unamused. “Why would I want to agree with that?”

“You… you wouldn’t have to worry about anyone walking in anymore,” you added quickly. “Since I’m usually the only one awake at that hour.”

He raised an eyebrow. “That’s not enough of a reason to involve us together.”

You felt heat rise to your cheeks. “It takes too long for me on my own. Doing it together… could save both of us time.”

Senku leaned back slightly, expression deadpan. “So you’re proposing time management… through a sexual intercourse. Brilliant. Absolutely not.”

You blinked, cheeks burning. “…I’m serious! Think about it. You get your stress out, I get un-horny. It makes sense.”

Senku stared at you for a long moment, expression unreadable, before letting out a sharp sigh. “No. Absolutely not. Your nocturnal ass is drowsy at 3pm. That brain reacts similarly to being drunk. You are literally impaired, and your judgment is completely unreliable right now. I am not listening to another word of this.”

You groaned, pressing your palms to your face, cheeks aflame. “…I'm still conscious,” you muttered, voice muffled.

Senku’s eyes narrowed, and he waved a hand dismissively. “Go on. Get out of here before I assign you another chore. And trust me, I will if you linger with more of these… hypothetical experiments.”

You let out a long, frustrated sigh and stepped back, retreating from the lab.

Chapter Text

Senku lay back, mind wandering as his hand moved absentmindedly on his hard member. “Technically, I could build a functioning vehicle from scratch in the Stone World,” he murmured, voice low to himself. “The real problem isn’t the engine or the wheels—it’s the exterior. Heavy materials give protection but slow down efficiency; lighter ones like plastic risk structural failure under heavy loads. Hmm…”

His gaze drifted toward the trapdoor by him, thoughts flickering between practical calculations and… less rational distractions. 

What if she crawled over seductively and took me in her mouth? 

The image was brief, unbidden, and yet it made him shudder. 

He let out a sharp exhale, hand slowing slightly. “…the theoretical limits on—” He paused, muttering under his breath, “…why am I even thinking about this right now?”

Senku decided to shelve the thought for tomorrow and tried to sleep. His body, however, had other plans. Minutes passed, and there was no sign of relief in his throbbing cock. With a resigned huff, he sat up, gripping himself. 

One of those times… just gotta rub it out.

Instantly, an image flashed. Your hands, so sure, so attentive, stroking him. Your shy face looking at him, asking if you’re doing it right. He shook his head, trying to clear it, and started again, methodical, calculated.

Twenty minutes went by. Nothing. The stubbornness was impossible to ignore. Finally, he let out a frustrated groan. Of course. This is your fault, he admitted to himself, jaw tightening. Every pulse, every twitch reminded him that his body refused to cooperate because of you. Because you brought up the idea of helping each other when he was so obviously touch deprived. 

Senku planted his feet on the floor, jaw set. Enough was enough—he was going to ask you. Might as well get it over with, he muttered, rubbing his temple briefly before heading toward the lab.

He opened the door, and there you were, meticulously conducting electrolysis on multiple beakers of sodium chloride, just like he instructed.

You glanced up, brow slightly arched. “Need something?”

Senku’s eyes flicked over the table, noting the freshly arranged electrodes, the beaker perfectly centered, and the clamps secured. “Hey,” he greeted, crossing his arms. “You’ve just finished setting everything up. Good timing.”

He leaned closer, voice dropping into that distracted, almost muttering tone he reserved for calculations. “With the voltage we’re using, it’ll take a few hours for a complete reaction.”

You tilted your head, hands stilling slightly on the apparatus. “I thought I followed your notes exactly… did I miss something?”

Senku shook his head, his usual sharpness edging his words. “You didn’t. It’s just the limit of these primitive batteries. No amount of tweaking’s going to change the fact we’re bottlenecked by their capacity.”

“Oh,” you murmured, letting go of the beaker, relieved.

He leaned back against the table, arms loosely crossed, his gaze still on you. “So, what were you planning on doing in the meantime?”

You shrugged, casual. “Since winter’s creeping up, I figured I’d go restock on coal. Better to get ahead of it.”

He scoffed, sharp and dry. “Like hell you would. You don’t have Magma’s brute strength or Chrome’s rock-brain encyclopedic nonsense. You’d get lost before you even found the coal. Hell—” his mouth quirked and he tapped his index finger on your forehead, “you don’t even have a headlamp.”

The words dug under your skin, pulling back a memory you’d rather bury. Heat prickled across your cheeks before you could stop it. You scratched at your arm, forcing a weak little laugh. “R-right… about that… haha, sorry. For… y’know. Overstepping.”

Senku only shook his head, a soft snort slipping past his lips. “That’s what I came here for,” he said, eyes narrowing on you with unnerving calm. “Do you still think that you could help me—” he paused, tilting his head slightly, “—by having sex, I mean.”

Your head snapped up. “Like—now? Right now?”

Senku sighed, dragging a hand down his face. “Optimally. My body refuses to clear the damn brain fog.”

Your eyes, almost against your will, trailed downward. “…Wait. Are you…?”

His gaze cut to you immediately. “I have been. For hours.”

Your eyes widened, voice squeaking before you could steady it. “Seriously—hours? Did you try to—”

“Yeah.” He cut you off without hesitation. “Tried ignoring it. Tried cold water. Even tried jerking off. Nothing worked.” He clicked his tongue, shoulders tightening as though admitting this was the most irritating experiment failure of his life. “The thought of sex just kept polluting my mind as the only viable release.”

You blinked, heat rushing to your face. “That’s… uh…”

Senku’s sharp eyes flicked toward you, catching every twitch of your expression—how your cheeks dusted red, the way your hands fidgeted like you were trying to act composed but failing. He turned away with a dry exhale, shoulders stiff. “Forget it. If you’re already second-guessing, it’s fine. Don’t force yourself.”

Your fingers shot out before you could stop yourself, wrapping around his wrist. “W-wait.” The word tumbled out shaky, almost swallowed. You couldn’t meet his eyes as you mumbled, “I… want to do it.”

Senku’s steps stilled, his features eased.“It’s honestly fine,” he said, glancing at you. “Don’t go out of your way.”

You forced yourself to look up, even though your face burned. “I’m not. And I'm not drunk. Or half-asleep. I’m saying this because I want to. I really… want to have sex with you, Senku.”

That finally got him to face you fully. You let go of his wrist, the silence between you stretching thin.

His lips quirked faintly, humourless. “Just don’t expect any princess treatment out of me. I’m not that kind of guy.”

You lay back on the blanket, the fabric scratchy under your skin, fidgeting with the edge just to keep your hands busy.

Senku crouched down, bracing one hand on the ground as he hooked the other under your knee. With a sharp tug, he pulled you closer until your leg rested against his hip.

Your breath hitched. You turned your face away, heat crawling up your neck. 

He noticed immediately. “What’s with that face? You’re not chickening out now, are you?”

Slowly, you forced yourself to look at him. “I’m not,” you blurted, voice louder than intended. Then, quieter but firm, “I… I want to do this.”

Almost on cue, your fists balled into the blanket beneath you, knuckles tight. 

Senku’s eyes flicked down at the motion, then back up to your face. “You’re a virgin, aren’t you?”

You let out a nervous laugh, trying to mask your embarrassment with sarcasm. “Y-Yeah. So what? Sue me.”

His lips tugging into the faintest frown. “Most girls talk about tears, candlelight, dramatic speeches about ‘first times.’ You’re really sure you want this to be your grand moment?”

You shot him a look, face still blazing. “I’m lucky enough to have sex before dying of polio in this world. I’ll let the roses and choir slide this time.”

Senku studied you for a long moment, then leaned down without warning. His lips pressed to your cheek gently, lingering just a fraction too long to pass as casual.

Senku’s lips curved faintly as he pulled back, his tone wry. “Here. Your debut beats half the pathetic first-time stories out there.”

You let out a breathy laugh. “Sorry you had to lower yourself to my silly emotional needs instead of going ahead with your sophisticated chemical ones.”

Senku chuckled. “Honestly, I’d prefer to let my brain have the chemical gratification as soon as possible.”

But then he leaned closer, nuzzling into your shoulder. “Although… skin contact alone triggers a flood of neurochemicals. Mostly useless, but surprisingly distracting. A good temporary solution.”

Your breath hitched, body tensing under his careful nuzzles. You instinctively pressed closer, feeling the warmth of him against you, heart hammering erratically. 

His lips brushed along your jaw and down your neck, careful, yet sending every nerve in your body alight. You felt your breath shorten, heart rate spiking under his measured observation.

He mumbled against your skin, as if noting your reactions like data points. “The body’s response… predictable, yet interesting.”

You blinked at him, cheeks flushed, trying to gather words. “…Senku… you’re teasing too much,” you managed, though your voice trembled, betraying how much the contact was affecting you.

He pressed a kiss lower, on the exposed breast from your loose shirt, then tilting his head back to study your expression. “Hm? Is the poor little baby feeling shy?”

You froze, heat spreading to your ears. “…Poor little baby?!”

“Mhm. Familiar, playful names increase oxytocin release,” he said, voice sliding into that teasing, gentle cadence, almost like he was talking at you rather than to you.

Your face burned, heat pooling in your stomach, as you realized how caught between embarrassment and desire you felt. “Stop pretending to be all so sweet, you prick.”

Senku only hummed, unbothered, before pressing his index finger against your clit through the thin barrier of your underwear. The pressure was maddeningly precise, deliberate.

He tilted his head, voice dropping into a low, mockingly gentle lilt. “Oh? Do you want to skip all the pleasantries then, sweetheart?”

Your hips twitched without permission, betraying you as your thighs quivered under his touch. “What, have you always been a sadist, or are you just putting on a show for me?”

A chuckle slipped past his lips, amused and unhurried. “I could ask the same.” His eyes gleamed as his finger pressed a fraction harder. “Have you always been an annoying brat, or is it just tonight?”

Heat flared up your neck. “I’m not a brat,” you shot back, your voice a touch too defensive.

Senku leaned closer, his breath warming on your collarbone as he dragged the circle just a little slower, savoring your reaction. “Hn. Could’ve fooled me.”

His touch shifted suddenly, the circling pressure leaving you empty before you could stop the whimper that slipped out. Two long fingers slid inside you instead, maddeningly slow.

“If you’re really not a brat,” he murmured, voice dipping with that mock-caring cadence he used, “Then prove it. Convince me that you want to keep going.”

Each second felt like a taunt, like he was dissecting your reactions with his crimson eyes.

You bit your lip. The excruciating slow speed of his fingers and the movements purposefully avoiding that spot made you think twice about showing any defiance. 

Your breath stuttered as you gripped the blanket beneath you, “Please.” The word slipped out sharper than you meant, so you rushed to soften them, voice dropping into something almost formal. “…Could you… go faster? Please.”

Your chest rose and fell too quickly, each shaky breath betraying how badly you needed it. You couldn’t bring yourself to meet his eyes, but you didn’t care; every part of you wanted him to hear exactly how much you needed this.

“That’s good,” he muttered on your skin. His pace shifted, the slow movements turning progressively faster. 

“Smart,” he teased, “asking for it right away.”

You couldn’t stop the small gasp that slipped past your lips, and your head tilted slightly into him despite yourself.

He titled his head, lips brushing your ear. “You’re making it way too easy to tease you,” he murmured, “with those little sounds.”

Slowly, he pulled his fingers back, the slick still glistening. He pulled back with a smirk, he wiped it on your thigh, voice dropping into that familiar dry tone. “See this? Your body produces it exactly like this when it’s ready. Nature’s lubricant, signaling prime conditions for mating. Extreme arousal.”

You flushed, a shiver running through you from the sensation on your leg. “…So… are we ready to start?” you asked, voice tinged with nervous anticipation.

Senku raised an eyebrow, smirk tugging at his lips.

“Impatient, much?” he teased, sliding his fingers back into position. “It’s important to properly prepare, especially since you’re a virgin. Rushing this step would be idiotic.”

You clutched his forearm as the build up started slowly increasing again. “Sorry… for making it too much work for you.”

He shook his head, voice low and amused. “Work? Hardly. I’m enjoying this. It’s honesty incredible how textbook you are.”

Senku adjusted his angle slightly. “This part here? Just the canal. But if I curl my fingers approximately two inches…” He slowly curled them, and a sharp gasp escaped your lips.

You couldn’t stop the shiver that ran through your spine. “Senku… ngh~” you gasped.

His voice dropped to that soft, teasing lilt that always made your heart skip. “Funny how the girl who constantly bosses me around is now sitting so quietly under my fingers.”

You moaned, as he circled on your clit again.

“Maybe not so quietly,” he murmured with a low chuckle, spreading his fingers just slightly more. The slick sound was louder than anything you’d ever noticed before, and your body tensed. Tears welled in your eyes from the pleasure.

Senku tilted his head, watching you with mock curiosity. “Huh… think I’ve ruined your little attempts at touching yourself again?” His tone was half-amused, and you could feel the teasing in every word.

You flushed, words catching in your throat. “…Maybe…” you admitted, looking at him with teary eyes.

“Good,” he murmured, pressing a little deeper and spreading his fingers just enough. “The way your body produces—no, not just produces, synthesizes—pleasure signals, dopamine, oxytocin, all of it, and I just… I want you to think of me while all of that is firing. Like, imagine I’m right here, helping optimize—no, enhancing—the whole process, making it faster, better, more precise, and—”

The build up was almost getting unbearable. Your hands shot up, gently pulling the back of his head toward you. Pressing your lips to the corner of his mouth, you cut him off with a soft, decisive kiss.

He froze immediately, his fingers slowing. Then carefully, he met your mouth directly with his own.

Yours lips felt so soft on his.

He couldn’t help the murmured commentary, soft and low against your lips.

“… it’s all these little transmitters firing… all of them telling your brain, ‘this is… pleasurable,’ even— wait—”

You kissed his lips again. 

He exhaled sharply, withdrawing his fingers and sliding his hand to your hip instead, grounding you with his grip. His lips pressed again, harder, hungrier now, the words dissolving into the warmth between you.

“…You know a kiss is just a useless stimulation,” he whispered against your mouth, a low confession. “But your brain—your whole body—can’t help but love it.”

You let out a shaky laugh, breath catching as you pulled back just an inch. “That’s… a lot of words for ‘Thanks for the kiss.’”

Senku pushed up on his hands, hovering above you. For the first time, you caught it—his composure cracked, the faintest color rising to his cheeks.

Your lips curved slyly as you reached up, brushing your thumb along his bottom lip. “Well, would you look at that. You actually look flustered, sweetheart.”

His hand shot out, catching your wrist with surprising gentleness, pinning it just enough to still your touch. His voice dropped, half-plea. “Shut up.”

“What’s the matter? Don’t like being on the other end for once?”

Senku’s eyes narrowed, the corner of his mouth twitching like you’d just set off a challenge. Without breaking eye contact, he dragged his tongue in one slow stripe along the inside of your wrist.

The sound that tore out of you was embarrassingly high-pitched, and you squirmed under him, face burning.

His chuckle was dangerous. “Think before you speak,” he warned softly, lips ghosting against your damp skin, “before I change my mind about going gentle.”

You forced a shaky laugh, even as your pulse raced where his tongue had trailed. “Alright, alright—you win. Are you finally done with your whole virgin preparation routine, professor?”

Senku leaned back just enough to look you in the eye, his smirk sharp and knowing. “Tch. Should’ve prepared you as a virgin sacrifice instead… the way you get on my nerves,” His gaze flicked over your face, lingering on your flushed cheeks and the heat swimming in your eyes.

Then he snorted, amused. “But the way you’re staring at me right now… looks like you’re about to pounce. Like I’m the damn virgin here.”

Your face went hot instantly. “N-no way. That’s you,” you shot back, your voice unsteady but defiant.

You jabbed his clothed length again with your foot, huffing. “See? You’re the one who’s worked up.”

Senku let out a low chuckle, not even pretending otherwise. “Yeah, no point denying it. You’re right.” In one easy motion, he caught your ankle, tugging you toward him until your hip brushed against his again. His grin tilted sly, voice dropping just enough to make your stomach flip.

“So, tell me—” he murmured, eyes glinting with amusement, “are you really okay with going all the way? Actually having sex with me?”

“…Yes,” you breathed, the word slipping out before you could overthink it. Senku slipped a hand under his drawls.

A second later, you felt it. His tip nudged against your cunt. Hot and leaking. Your gaze faltered, darting away as heat flushed up your neck.

Senku’s hand caught yours immediately, fingers weaving between yours until his grip was firm, grounding.

“Here,” he murmured, squeezing your hand just enough to draw you back. “Keep looking at me.”

Then he pushed forward, slow and deliberate.

Your breath stuttered into a half-gasp, half-whimper, your body tightening around the intrusion, sharp pressure blooming into heat. Your hand curled into his hand.

Senku’s jaw flexed, a low grunt slipping past his lips despite the way he tried to hold it back. “…Fuck,” he whispered, the sound strained, reverent.

Then slowly, carefully, he began to move—measured thrusts, deliberate patterns that grew into a rhythm. The sound of skin meeting skin echoed faintly in the room, embarrassingly loud, like it was announcing every motion.

Your breath kept catching in your throat, unsteady little hitches you couldn’t control. Each one made Senku press his forehead into your shoulder, his voice muffled against your skin when he finally spoke.

“…Tight,” he muttered, almost like he was thinking aloud, but his tone cracked with strain. “Hot. Like you’re molding yourself around me—hell…”

You let out a shaky breath, eyes half-closed, and murmured, “…I’m sorry…”

Senku pressed a soft laugh against your shoulder, shaking his head. “Don’t.” His voice was low, barely steady. “It’s good. You’re… good.”

All the careful prep made everything glide effortlessly. There was no pain, no sharp edges; only pure, unadulterated bliss.

Your hands clutched his a little tighter, and a small laugh escaped you, light and breathless. “…I’m glad you did all the work.”

“Told you… the preparation is necessary.”

Senku’s hands released yours just long enough to shift your hips, guiding them upward. The sudden depth made your chest hitch sharply, a startled gasp caught between your throat and the back of it. 

Senku’s eyes flicked to your face, taking in the flush rising across your cheeks, the tiny pout of your lips, the way your lashes fluttered like you were trying to hide but failing. “Huh… look at the state of you,” he murmured, “did it feel better?”

Your breath hitched, words tumbling out softer than you meant. “It does… it feels really good.”

He shifted just slightly, thrusting faster, deliberately. Your chest lifted sharply, a gasp tearing free. He caught the way you bit your lip, the small tremble in your jaw, even the sheen of moisture forming at the corner of your mouth.

“Perfect,” he whispered, almost to himself. “That face… it’s exactly what I wanted to see.”

You wrap your legs around his frame instinctively, a low groan escaping your throat. You try to say a protest, maybe, or beg. But the words get caught somewhere between your lips and your lungs.

“What, can’t even talk now? That’s fine… I get it.” His thumb grips along your side, but it sends shivers up your spine. “Women are… more sensitive than men, after all. Makes sense… you’re reduced to little noises.”

The combination of his words and the relentless, precise motion left you trembling. Your breath came in ragged, stuttering gasps, chest heaving, thighs quivering. 

Senku felt pity seeing you so overwhelmed. His rhythm shifted, easing just enough to let you catch your breath but still keeping the steady pull that made your insides clench. 

Even with the slight reprieve, your body still felt like it was buzzing from the overstimulation, every nerve taut and alive. “A-are you… not feeling what I’m feeling then?”

Your blurry vision cleared, your lashes lifting just enough to watch him.

“I don’t know,” he repeated breathily, his voice thick with disbelief. “I can’t imagine anything feeling better than this.”

His expression… it was raw. His mouth parted, breath ragged, his face flushed crimson. He looked less like the genius who always had control and more like someone overwhelmed, caught in a high he hadn’t anticipated.

You couldn’t help yourself—you wrapped your arms around his neck and dragged him lower, pressing him flush against you. His breath stuttered as he grunted, “You’re… clenching me so damn tight.”

Your fingers threaded instinctively through his hair, tugging without thought. The sound he made—half-groan, half-choke—vibrated right against your skin.

You laughed breathlessly through the haze, words tumbling out before you could stop them. “Hah… That’s your fault... for fucking me like a damn rabbit… in heat.”

“Let’s see,” he panted against your ear, “if you’re still running your mouth when I do this.”

He slammed against your g-spot again and again, the rhythm relentless. At the same time, his hand slipped lower, his index finger circling and pressing against your clit with ruthless precision.

Your grip on his hair turned desperate, knuckles white as you clung to him like a lifeline. Every thrust, every merciless flick of his finger sent shocks up your spine until you were unraveling, trembling under him.

“Senku—!” The word tore out of you, breathless, broken. “I—I’m gonna— I’m gonna come—” Your voice cracked, frantic, spilling out without restraint as your nails dug into his back through his clothes, dragging across the fabric like you needed something to hold you together before you fell apart. 

Your grip tightened in his hair, nails biting into his back as your voice broke apart. “Senku—I’m—ah—I can’t—!”

“Good,” he rasped, still thrusting deep, his finger rubbing circles. “That’s it. Let go.”

The wave crashed hard, ripping a cry from your throat as your whole body clenched around him. Your thighs trembled violently, every nerve sparking with too much sensation.

Senku groaned low, feeling you tighten around him, dragging him closer to the edge. “Fuck—you came…” His pace faltered, then slowed, riding out your shudders until you finally slumped back against the blanket.

With a final sharp thrust he pulled free, a strangled groan spilling from his throat as cum streaked across the bare skin of your belly where your shirt had ridden up and on it as well. His breath came ragged, uneven, slumping forward until he finally sat back, both of you drowning in the same heavy rhythm of panting silence.

Senku’s hands moved after a still minute, fingers working at the knot holding your shirt together. You grimaced, half-dazed. “…I’m not ready for round two.”

“Tch. Calm your over-imaginative mind,” he muttered, standing and folding the fabric neatly as he crossed the room. “I got it dirty. That’s all.”

You rolled your head on the pillow to watch him, your lips quirking. “It was a rather educated guess, though.”

He didn’t rise to the bait. Just came back with something in hand, and a moment later you flinched at the sudden wet, cool press of a rag across your stomach.

A dry laugh escaped you. “Didn’t think you’d be so kind with me after all that.”

He didn’t look at you, mumbling more to himself than anything else. “It’s basic sanitation.”

Senku tugged your undergarments back into place, then finally let himself collapse halfway onto you. His weight pressed comfortably against your frame, one leg sliding between yours, his arm anchoring you close.

You sighed, the warmth of his body lulling you. “…What, does this have a scientific explanation too?”

“Shut up already,” he muttered into your skin.

Normally you’d have a snappy comeback, but exhaustion pressed you down, stealing your fight. You only complied because your body begged for rest.

Senku shifted just enough to murmur, “I’ll deal with your clothes first thing in the morning.”

You rolled onto your side, coaxing him with you until you were facing each other. His eyes were still open, fixed on you. His face was unreadable, stoic as ever—but his gaze burned with quiet intensity, studying you like something he couldn’t quite quantify.

“You know,” you murmured, voice still hoarse from everything, “you had a really pretty expression earlier. When you looked… disheveled. Blissed out.”

Senku immediately rolled his eyes, scoffing. “Pretty expression? What are you, an idiot?”

He started to turn away, but you caught him with your words before he could.

“When we kissed. You made the prettiest face. I want to see it again.”

“You’re stupid,” he muttered, voice low. Then, almost imperceptibly, he added, “Next time.”

You let out a soft laugh, your eyelids feeling heavy. His gaze softened just slightly as you drifted off, the quiet weight of the moment settling around you.

—-

You woke up surprisingly early for your usual night-owl routine. As you sat up, the blanket slipped off, and you realized you were fully dressed. Senku must have put your clothes back on while you slept.

You let out a long yawn and stepped outside toward the common ground, the morning air crisp against your skin. Kohaku waved from nearby, a small grin on her face. “Hey, over here,” she called, holding out a fluffy pink stick of cotton candy. Chrome stood beside her, arms crossed and looking slightly amused.

“It’s rare to see you actually wake up at dawn,” Kohaku teased.

You shrugged, taking a tentative bite of the cotton candy. “I was completely spent after last night’s work,” you half-lied, hoping to keep the details vague.

Chrome nodded sagely. “Makes sense. Senku suddenly became… sharper. Like he’s two Senkus now. He’s been assigning tasks for multiple roadmaps like crazy!”

Kohaku smirked. “Sounds like someone’s slacking off, then.”

“I’m just waiting for the iron to cool,” he said dryly taking a bite of his cotton candy.

Kohaku rolled her eyes and pointed a finger at him. “Toughen up. You need to get used to the temperature.”

“That’s not how it works!” Chrome protested, waving his hands. “And how could an ordinary human touch something that hot, you gorilla!”

Chaos immediately ensued as Kohaku swung her fists. Chrome yelped, ducking and trying to defend himself, his protests drowned out by Kohaku’s wrath.

You stepped back, a small laugh escaping you as the commotion unfolded. Then your eyes caught Senku as he stepped out of the lab. He paused, glanced at you, and bent a finger in a slight beckon. You followed without a word, drawn in by that quiet command.

He tilted the cotton candy toward his mouth, taking a deliberate bite. 

Your voice caught in your throat, stuck somewhere between disbelief and awe at his sheer audacity. He noticed immediately, a small chuckle escaping his lips at your reaction.

“Word’s spreading,” you murmured, eyes glinting with amusement. “You’re officially the science machine now.”

He rolled his eyes, figuring out that you knew it was the byproduct of last night and you were here to tease him. He didn’t let you. “Go help Kaseki with the glassware.”

You blinked, completely thrown. You hadn’t expected a task of your own on top of everything else. Instinctively, you tried the tired card, dragging out your limbs with exaggerated weariness.

Senku leaned in, hand lingering on your shoulder. “Do as I say… and tonight, I’ll make sure you remember why being on my good side is worth it.”