#personal experiments

iii. Lessons in Anatomy

cws: alcohol consumption, implied voyeurism, bondage, power dynamics, fingering, praise, crying, slight worshiping, let me know if i missed anything!

4.9k words

The lab, as you realized, wasn’t an option for Senku’s bizarrely intimate “experiments” anymore. Too many close calls. Too many eyes. Too many chances for someone to put the pieces together if they looked closely enough.

You’d even teased him about it once—half-joking, half-serious—that if he had any more of his ideas, he’d need to find someplace else to conduct them. Preferably not a shared workspace.

You hadn’t thought he’d take you literally.

Which is why you froze when the knock came on your apartment door at 11 p.m. on a Friday.

You’d been perfectly content sprawled across your couch, tea in hand, hair loose, dressed in nothing but a pair of worn boxers and a faded T-shirt from a research convention you barely remembered attending. The night was supposed to be quiet. Yours.

Dragging yourself up with a groan, you padded barefoot to the door, already rehearsing the verbal lashing for whoever thought it was acceptable to bother you at this hour.

When you swung the door open, your irritation only spiked.

“Are you serious?” you demanded, glaring at the tall figure leaning against your doorframe.

Senku.

Of course, it was Senku.

He looked utterly unbothered by your tone, as if he had predicted it word for word. A bag was slung over one shoulder, the strap digging slightly into the line of his shirt, and in his other hand dangled a six-pack of beer. His lips tugged upward, faint but smug, like he already knew you wouldn’t turn him away.

“Evening,” he said simply.

Your eyes dropped to the beer, then to the bag. Suspicion curling tight in your stomach. “Don’t tell me you dragged yourself all the way over here just to freeload.”

“I could,” Senku replied easily, his smirk deepening. “But you’d know I was lying.”

You crossed your arms, leaning into the doorframe with deliberate defiance. “So what then? You staging a heist? Because you’re late enough to get away with it.”

“I came with a purpose.”

You crossed your arms over your chest, blocking the doorway with your body. “A purpose. Last time you said that, you nearly fried my nervous system.”

“Which was a success,” he countered smoothly, eyes gleaming with something far too entertained for your liking. “Tell me you didn’t enjoy it.”

You scowled, “Get to the point, Ishigami. What’s in the bag?”

His red eyes gleamed in the dim hallway light, sharp and amused. “Rope,” he said, blunt and shameless, as if announcing the weather.

The word dropped heavy between you, enough that for a split second, you swore your neighbors could hear it through the walls. Heat creeping up your neck, but you masked it with a scoff, fighting the instinct to glance down the hall.

“You’re unbelievable,” you muttered, though you stepped aside, swinging the door wider in reluctant invitation.

Senku walked past you without hesitation, like he’d been here a hundred times before. He set the beer on your counter, then crouched to unzip the bag, rummaging with the same focus as someone unpacking lab equipment.

You, meanwhile, made a beeline for the six-pack—anything to ground yourself. You yanked a can free, the aluminum cool against your palm, and cracked it open. The hiss of carbonation cut sharply through the quiet of your apartment, loud enough that it made you flinch.

You tipped it back in one long swallow. The taste hit instantly—cold, crisp, the faint bite of hops carving through the malty smoothness—your favorite. The bitterness curled across your tongue, sharp enough to distract you for a fleeting second, but the burn of it sliding down your throat did nothing to steady your pulse. But the burn sliding down your throat did nothing to slow the hammering of your pulse. If anything, it seemed to sharpen it, each beat echoing in your ears.

Pulling the can away, you caught yourself staring at the label, then glanced over at him. “Oh. I like this brand.”

“I know,” Senku said without looking up, voice calm, assured—like the fact had been obvious all along. “That’s why I got it.”

The words landed heavier than they should have, dropping like a weight into your chest. You hated the way your stomach flipped. Hated more that he had noticed enough to bring it.

You took another sip, slower this time, but it did nothing to settle the warmth creeping beneath your skin. “You’re… way too observant for your own good, you know that?”

His smirk deepened, faint but smug, eyes glinting from beneath his lashes. “Occupational hazard.”

You leaned against the counter, beer cool in your hand, watching him with a wary eye as he unzipped the bag with a methodical precision that was all too familiar. His focus was unnerving—calm, exact, as though unpacking your kitchen table was no different than laying out samples in the lab.

Except instead of glass slides and wires, what landed neatly on the cold marble counters were coils of rope. Soft-looking, but thick. The vibrant red color of them only made them stand out sharply against the pale surface of your table.

You took another long drink, the carbonation fizzing against your tongue, as if the taste could mask the sudden, restless flutter low in your stomach. “You just have this lying around?”

Senku didn’t even glance at you. “Of course not. I bought them specifically for tonight.”

You raised a brow at that, pulling the can away from your lips. “Where the hell did you find these?”

“Some shibari store near the station,” he replied casually, as though discussing where he’d picked up his groceries. “Nothing wild. Though, admittedly, the clerk gave me some strange looks while I was deciding.”

“Go figures. I mean, it’s not every day you see the great Senku Ishigami in a BDSM store.”

Senku finally glanced up, one corner of his mouth tugging higher. “She probably thought I was wasting her time. But I walked out with exactly what I needed, didn’t I?”

You tilted your can toward the coils on the table, arching a brow. “Bold of you to assume I’m just gonna let you test-drive that on me.”

His smirk sharpened, the kind of look that made your stomach twist in ways you didn’t like admitting. “You and I both know that’s a lie.”

You grumble a low sound of “cocky bastard,” under your breath, but he doesn’t take the bait. You crossed your arms, watching him coil the rope with unnerving precision. “Well?” you prompted, voice sharp but teasing, taking a step closer. “Are we just gonna stand here, or…?”

Senku’s smirk deepened, silent and patient. “Or…?” he echoed, voice low, each word dragging like a dare.

“You know,” you said, letting the words hang, “maybe we should… go somewhere a little more comfortable. Your experiments tend to need space.”

He let out a soft, amused hum, eyes gleaming. “So impatient. If I didn’t know any better, I’d assume you want this.”

“Don’t give me that shit,” you shot back, a corner of your mouth twitching, “I’m just trying to hurry this up so I can get back to enjoying myself.”

“You’ll be enjoying yourself soon,” he said, voice dipping just enough to make the words hover between promise and something far more suggestive. The smirk never left his face, and the calm certainty in his tone made your pulse stutter in response.

You huffed, arms still crossed, but he didn’t wait for a response. With a pep in his steps, he started walking toward your bedroom, the rope in his hand swinging lightly with each step. You followed at a measured pace, though your gaze kept flicking down, betraying your curiosity.

The doorway to your room loomed ahead, dimly lit by the bedside lamp. Senku paused for a moment, taking in the scene—the unmade bed, your cluttered vanity, the books missing from your bookshelf. His eyes lingered, sharp and calculating, soaking in the space, and you felt yourself getting flustered.

“Stop gawking, genius,” you jabbed, trying to break the tension, your voice sharper than you intended. “Your virginity is showing.”

Senku’s smirk deepened, a flash of amusement in his eyes. “Funny, coming from someone who’s clearly been anticipating this more than they’ll admit.”

You opened your mouth to retort, but before a word could leave, he was behind you. The warmth of his body pressed close, the air between you thickening with unspoken tension. Instinctively, you stepped back, matching his approach, a silent dance of push and pull.

Each step he took made your pulse stutter, your fingers curling slightly as your knees pressed against the corner of your bed. You stumbled just a little, letting yourself fall onto the mattress with a soft thud, the sheets bunching beneath you.

“See,” he murmured, voice low and teasing, “I knew you were eager.”

You bit back a sharp retort, chest rising and falling fast. “You practically forced me here!”

Senku only chuckled, the sound low and knowing. The rope in his hands seemed almost incidental now, secondary to the magnetic pull of him, the way the space between you charged with anticipation as your eyes locked.

“You’re always so tense,” he murmured, voice low, almost casual, as he stepped around to hover near your side. “I thought you’d be used to this by now.”

You tilted your head back, gaze sharp and unamused despite the flush climbing your neck. “You barge into my place late at night and proposition me with bondage. I’d be more surprised if I wasn’t tense.”

A smirk tugged at the corner of his lips, and he didn’t respond, only letting his fingers trail along the rope before finally looping it around your wrists. The soft brush of his hands made your pulse stutter. “Relax,” he murmured, almost under his breath, “this isn’t going to hurt… unless you make it hard on yourself.”

You swallowed hard as the rope brushed your skin—coarse, fibrous, catching faintly on the tender inside of your wrists. He gave it a small tug, testing the tension, and the sound it made was almost obscene in the silence of your bedroom.

“Is that too tight?” Senku asked, his tone maddeningly neutral, like he was calibrating an experiment rather than tying you to your own bed.

“I don’t think so…?” you said softly, uncertain.

His gaze flicked up to meet yours, sharp and unyielding. “It’s a yes or no question.”

“Then no,” you muttered, rolling your eyes up at him.

The corners of his lips tilted downward in mock disappointment, though the gleam in his eyes betrayed him. You tear you gaze away as you let out a dejected sigh:

“No, sir…”

“Better,” he replied, satisfaction reflecting from his gaze.

Knot by knot, he worked with maddening precision. Each twist of rope snug against your skin, methodical, measured—like he was documenting every reaction you gave him in the private notebook of his mind. When your wrists were bound neatly together, he lifted them toward the headboard, looping the rope through and anchoring you in place. The movement pulled your arms up just enough to arch your back, leaving you stretched in a way that made you far too aware of how exposed you are.

“You better not scuff my headboard, genius,” you bit out, glaring at him through the faint blush rising to your cheeks.

Senku let out a quiet chuckle, the sound low and infuriatingly amused. He gave the rope another quick tug, just enough to jolt you against the bindings. “You’re really worried about furniture right now?” He tilted his head, red eyes narrowing in something that hovered between curiosity and taunt. “Typical.”

“You’re lucky I’m even letting you—”

Your protest cut off with a sharp gasp when his fingers ghosted down your side. Slow, exasperatingly slow, trailing from the sliver of exposed skin from when you fell back on the bed, to under your shirt, up along your ribcage. The touch was deceptively light, almost clinical, as though he were mapping your body the way an astronomer would map a constellation—measuring, cataloguing, memorizing—as if he were testing how well you could squirm with your arms bound.

The rope amplified everything. Every brush of his fingertips felt sharper, every shift of the sheets louder, every breath caught in your throat impossible to disguise. You tried to hold still, but your hips shifted restlessly against the mattress, wrists flexing uselessly against the bindings.

Senku’s eyes glittered as he watched you squirm, the corners of his mouth curling upward. “Good. You’re already moving more than you realize.” He leaned closer, close enough that you could feel the warmth of his breath against your temple, his voice dropping low.

“This will be a very… thorough experiment.”

The rope held firm, your arms useless against the headboard. Senku hadn’t done much—just the occasional graze of his fingertips along your side, a feather-light brush over your hip, the deliberate drag of a knuckle down your thigh. But each touch felt amplified under restraint, sharp and humming, as if your body had nothing else to focus on but him.

It wasn’t even overtly sexual, yet it was maddening in its subtlety, the way he traced you like he was memorizing topography, like every shiver you gave was another data point.

His palm spread fully against your thigh. Warm, steady fingers pressing into the soft flesh as though testing its give. He dragged upward slowly, the path firm but unhurried, until his thumb brushed dangerously close to the hem of your boxers. The simple motion sent a shock through you, and he stilled, gaze snapping up to your face as if cataloguing the reaction.

His gaze lingered. Not just on your expression, but on all of you—your shirt, now slipping off your shoulder, the worn cotton stretched across your chest, the bare skin of your legs laid out before him. For once, his composure cracked, the faintest flicker of something raw flashing across his features before he caught himself.

Your breath hitched. “What?” you demanded, voice sharp to cover the tremor. “Is something wrong?”

For a moment, you thought he might untie you. That he’d decide you’d gone too far. That maybe this was the end of whatever line you’d both been toeing.

But then he moved—fast, decisive—leaning in until his breath fanned hot against your ear. His nose brushed along the curve of your jaw, and then lower, into the soft space of your neck.

“Senku—”

Your voice broke into a gasp before you could stop it, a mixture of surprise and protest that only seemed to embolden him. His mouth ghosted over your skin, feather-light at first, teasing, the brush of his hair against your cheek adding to the dizzying intimacy. The scent of him filling your lungs.

It was too much.

When he lifted his head, his eyes scanned your face, unreadable and sharp, flicking between your parted lips and wide, flushed eyes. There was a calculation there, as if he were weighing every risk, every impulse, every possible step you’d take next. And yet, beneath the surface, there was something else—a flicker of desire he hadn’t bothered to hide.

Then, just when you thought you might survive the anticipation, his lips pressed against your neck. Light, fleeting, almost a tease, but enough to make you nearly jerk against the restraints. The rope held you firm, wrists aching just faintly under the pressure. A sound slipped past your throat before you could stop it—half gasp, half protest.

“Stop squirming,” he murmured, though the rasp in his voice betrayed him. It wasn’t steady. Not the even, clinical cadence you were used to hearing from him. There was a crack in it now, low and rough, as if he wasn’t quite immune to the same burn he’d set off in you.

You wanted to snap back, to throw some biting retort that would reassert control, but your tongue stalled when he pulled back just enough to look at you. His gaze caught yours, burning and unflinching, a scientist mid-discovery who suddenly realized he might not be able to control the outcome of the experiment. His eyes dragged lower—down to your parted lips, the flush climbing your cheeks, the way your chest rose and fell too quickly.

The silence stretched between you, fragile as spun glass, until he finally gave in and closed the distance.

The kiss wasn’t careful. It hit you like a spark to dry tinder—hungry, frustrated, a sudden shattering of the restraint he’d been holding onto. His mouth claimed yours with startling certainty, and you arched up into it before you could think better of it, kissing him back with equal fervor. Every nerve lit like fire, the rope biting into your wrists when you instinctively tried to reach for him.

The mattress dipped as his weight shifted over you, creaking beneath the push and pull. You twisted against the binds, the cords digging into your skin with each futile tug, but even the faint burn of friction only sharpened the heat between you. His mouth found yours again, ravenous, and demanding, and the taste of you— tinged faintly with the bitter tang of beer—flooded his senses. It was dizzying, grounding, and intoxicating at once.

His hand slid to your hip, palm broad and steady, anchoring you against the restless roll of your body. The other tangled in your hair, tilting your head back to deepen the kiss, and his precision was maddening—every nip, every drag of his tongue mapped like data points, but desperate in a way that betrayed intent. He wasn’t just recording your reactions. He was chasing them.

You kissed him harder, meeting every press with your own, teeth grazing, lips bruising, both of you moving in a rhythm too rough to be called controlled. The sheets twisted beneath you, the air between you hot and short, and all at once the line you’d both been toeing dissolved completely.

Senku’s hands slid up your sides, fingers grazing and gripping the soft fabric of your shirt as if it were the only thing keeping him tethered to reason. His lips barely parted from yours, brushing with that familiar mix of heat and insistence, before he murmured against your mouth, “Can I?”

The word was low, almost a growl, carrying a desperation that was completely uncharacteristic—and entirely magnetic. “Please…” he added, the growl threading through the plea, vibrating against your lips in a way that made your pulse stutter.

You closed your eyes, caught somewhere between heat and trust, and nodded almost frantically. Your hips lifted slightly, an unconscious signal, making it impossibly easy for him to inch the fabric higher.

His hands hover at your waist for a moment, thumbs brushing the edges. Then slowly, he pushed it up, revealing the creamy expanse of your breast, the mint-green lace of your bra coming into view. The soft light of the bedside lamp caught the delicate embroidery, and the contrast against your skin made the sight feel almost surreal.

He didn’t move his gaze. The quiet awe in his eyes was almost tangible as he watched your chest rise and fall, the subtle jiggle from your restrained movements catching his attention. Every tiny shift, every micro-reaction you made, seemed to imprint itself in his mind—he cataloged it instinctively, but there was something more beneath the scientific detachment.

Then his hand moved, large and confident, cupping your breast, his fingers and thumbs kneading the soft flesh. You gasped as the sudden coolness of his hand met your heated skin, nipples stiffening instantly under his touch.

Leaning closer, he took one straining peak into his mouth, suckling and swirling his tongue around the sensitive bud. You arch up against him, a sharp, breathless little moan escaping your lips. The sound only spurred him on, and he alternated attention on one breast, then the other, until they were glistening and aching for more.

Even as he worked, he began to murmur a stream of scientific facts, his deep voice vibrating against your skin. "Nipples are highly erogenous zones. They contain over 800 nerve endings, making them extremely sensitive to stimulation. The areola—the dark skin surrounding the nipple—contracts and expands in response to arousal."

“Fuck— you think… I dont know that already?” you managed, cheeks burning, breath uneven. Trying your hardest not to draw attention to your clenching thighs

“Oh, I’m sure you do,” he said, a smirk curling his lips. “It's just interesting to see how textbook your responses are.”

His hands lingered a moment longer before sliding down to your hips, palm pressing warmly against the supple skin, fingers tracing slow, exploratory patterns as if memorizing the contours beneath his touch.

He paused, glancing at you with that same sharp intensity, then lowered one hand a little, letting his fingertips brush over the waistband of your boxers. The movement was hesitant, almost questioning.

“Is this okay? He asked quietly, like he was just as aware of what he wanted as you were.

You felt heat pooling between your legs at the touch, twitching involuntarily. “Yeah… It’s fine,” you said, your tone steady even as your body betrayed you. You shifted your hips up to give him easier access.

Senku’s fingers traced the edge of your underwear before tugging them down in one swift motion. They pooled at your ankles awkwardly, but you didn’t dwell on that for long, the cool air now hitting your now exposed cunt, sending shivers down your spine.

Your hips were shifting on their own, every one of his touches feeling more intense than the last. You knew it was due to blood rushing to the region, making your nerves insanely sensitive. He just stared.

“Fucking pervert." 

A low, familiar snicker filled the room, his amusement palpable. "aww, you caught me," he said, voice calm but laced with that sharp undertone that made your stomach twist. His finger pressed lightly against the hood of your clit, teasing back just enough to make your knees tremble. The sensation forced a soft, involuntary gasp from your lips.

“Although you seem to be enjoying yourself as well,” he murmured, “This part of you… It's become nice and swollen."

His thumb began to make slow, deliberate circles over the sensitive nub, and your back arched instinctively, wrist straining against the restraints.

"This little thing has more than 6 times the nerve endings of a penis—and that’s just the tip..." his voice rough and even.

You tried not to cringe at the textbook phrasing, at the absurdity of an anatomy lecture against wet heat pooling between your legs, but he didn’t pause, didn’t care.

His other hand slid down, dragging along your folds, spreading them gently, exploring, while his first continued teasing over your clit. Then, with clinical precision, he guided a finger to your entrance, pressing just past the threshold, testing, mapping, and drawing out your reactions.

Your body responded before your mind could catch up, hips lifting, back arching, every nerve alight, your soft whimpers and shivers marking his every success.

Finally, he sank his finger fully into you, inch by inch, until he was knuckles deep. His gaze locked onto yours, sharp and assessing, as if checking for permission—or discomfort. You offered a slight nod, letting him know it was okay.

Then he began to move—slow, measured thrusts at first, each deliberate. Your body clenched. Every push, every flick of his wrist, every glide of his thumb against your clit was calculated to heighten the sensation.

He leaned into you, chest brushing yours, heat radiating off him as he continued. Fingers moved in tandem, thumb circling with cruel precision, probing, testing, teasing.

You were trapped, restrained at his mercy, and every movement, every touch, every sensation made it impossible to think, only burn and shiver and arch, lost in the overwhelming intensity of being exactly where he wanted you.

“Mmph—Senku—I’m so…” The words broke off into a gasp, swallowed by a shuddering moan as your body tensed and released

“Shhh… It’s ok,” he cooed, “You can cum.”

And then it happened. The tight coil inside of you snapped, silling over in waves that crashed throughout your limbs. Your back arched violently, hips pressing against the mattress, wrists straining uselessly against the binding. Breath catching in ragged gasps, chest rising and falling fast.

Senku’s hand remained firm, holding you just enough to help you ride out your high. His thumb still circled with patient precision, each motion coaxing more whimpers and moans from your lips. “Good job,” he murmured, tone low and approving.

Your eyes rolled back as the last waves of pleasure passed through you. Even while bound, flushed, and spent, you were acutely aware of him—of the way his gaze followed every flicker, twitch, and shiver.

“The usual refractory period lasts a few minutes,” he said, voice clipped—far too detached for what he was doing to you— but there was a rasp in it now, rough and betraying. “But with the way you’re dripping, I doubt you’ll need that long.”

Your only answer was a frenzied nod, your voice lost to garbled sounds that tumbled helplessly from your lips. Your body said more than words ever could—hips twitching, chest rising and falling in frantic rhythm, thighs trembling where they strained against the sheets

Senku didn’t hesitate. His fingers dragged once more along your folds before pushing inside, this time, with two fingers. The stretch stolre your breath, the swet ache of it blooming hot and raw inside of you. You gasped, head falling back, mouth open as a strangled moan broke free.

He doesn’t give you time to recover. His pace was steady but unrelenting, each thrust of his fingers deep and exact, curling and prodding at your most sensitive spots that make you clench around him. His thumb went right back to its torturous flicks, the dual sensation forcing you the writh helplessly, your wrists straining against the ropes that held you down.

The wet, obscene sounds of his fingers working you open filled the room, accompanied by the desperate chorus of your cries. You couldn’t hold them back, couldn’t even think to try— your cries came shameless, raw, a symphony of pleasure that only spurred him on.

Tears prickled at the corners of your eyes, sliding hot down your cheeks. But even your tears felt inconsequential compared to the waves of bliss building inside of you, cresting higher and higher with every stroke. His mouth found your ear, lips closing around the shell as his breath scorched your skin.

"Look at you," He chuckled, his voice a low, rough rasp. "The way you respond to each thrust… honestly, it's distracting how gorgeous you are.”

“Senku—please!” Your voice broke, trembling somewhere between a plea and a scream. You weren’t sure what you were begging for, but he seemed to know. His pace fastened, fingers pistoning deeper, rougher, harder.

“Perfect,” he mumbled, awe flickering in his tone. “Squeezing around me so tightly… you’re absolutely perfect.”

That coil inside you snapped without warning. Your body bowed, ropes biting into your wrists as you came undone a second time. The climax tore through you violently, shattering you, dragging broken cries from your throat as your walls convulsed around his fingers.

He held you steady through it, thumb never faltering on your clit, his other hand bracing your hip, keeping you grounded through every tremor. Only when your body went slack beneath him did he finally slow, easing his touch until you were left twitching in the aftershocks.

Your breath came shallow, uneven, every limb heavy and uncooperative. You barely registered him moving until the ropes gave way, one knot after another loosened with careful precision. Your arms fell limp, but Senku was there, catching them, rubbing warmth into your sore wrists with a tenderness that contrasted the earlier rigor of his touch.

"Easy," he said softly, voice stripped of mockery now. His gaze lingered on you, sharp and unyielding as always, yet softened by something quieter.

Then his lips found your skin. A kiss at your jaw, then your throat, then the curve of your sternum. Slow, deliberate, each one paired with a low whisper of praise. “Good… so good… perfect.”

Too dazed to speak, you let out faint whimpers at his touch, your body twitching with every brush of his mouth.

He pulled back only long enough to clean you, movements efficient but careful, every gesture threaded with tenderness.

You slipped under quickly, body spent and heavy, fingers twitching until they found him. Even in your exhaustion, they curled into his shirt, clinging as if you couldn't let go.

Senku lay beside you, the heat of your body pressed into his side, your quiet breathing loud in the stillness of the room. He was aware of every ache in his own body, the rigid strain still pulsing insistently in his pants. He could deal with that later.

For now, his mind turned restlessly—variables, consequences, possibilities of what this meant. Of what you meant. Of what line they had crossed, and whether it could ever be uncrossed.

But he just lets out a heavy sigh. He’ll let it go—just for tonight.

Instead, he shifted closer, pulling you snug against his chest, his arm circling your waist. He pressed his cheek to the crown of your head, exhaling another breath he didn't know he'd been holding.

And for once, the genius allowed himself stillness.

He held you as you slept, and though his mind refused silence, his body stayed anchored by you.

an: they make me sick (affectionately)

the tension was killing me, I couldn’t hold off on it any longer… i’m sorry. lowk gonna be a slow week, my next post might be my last until october 5th. But we’ll see… sometimes visions speak to me 🤫

don’t wan't to share too much... but I've had this idea brewing for a while 😈

peep the new layout!! @mono-no-aware-stuff told me about ellipsus and I feel like a changed woman.

very rough first draft and it's going to change a lot before the final post but it shows a general idea of the direction i'm taking.