Work Text:
It had started with a challenge.
“There is no way anyone can actually do that without snapping their spine, especially you,” Chrome gestured at the sketch Yuzuriha had drawn in the dirt: a human figure bent nearly fully over backwards.
“Oh ye of little faith,” Gen replied, tone light and teasing, “you wound me with your skepticism.”
Kohaku rolled her eyes, “No way you can bend yourself like that. You can barely lift anything heavier than a cup of tea, let alone support your own body weight.”
“No, really,” Yuzuriha cut in, using the stick she had drawn with to poke at the doodle, “I saw him do it on TV once during an interview.”
“See?” the mentalist preened, “Yuzuriha-chan has seen me do it. You believe her , don’t you?”
Chrome crossed his arms over his chest, “I’ll believe it when I see it.”
Gen stared him down for a long calculating moment before shrugging his shoulders. “So be it. Taiju-chan, be a doll and hold this for me.” He slid out of his jacket and handed it to the taller man, and, after a moment of consideration, he also untied his obi and shrugged out of his yukata, leaving him in his trousers and lace up top. He rolled his shoulders a few times, shifting his weight from foot to foot as he centered his breathing, barely noticing the approaching footsteps as he began to move.
“What’s going on over… here…?” Senku had walked up just in time for Gen to fold forward, forearms braced on the ground as his feet lifted up behind him into a graceful forearm stand.
“Just giving the people what they want, Senku-chan~” Gen didn’t even sound out of breath, allowing his legs to bend at the knee, his back arching in an elegant crescent shape until his toes just barely brushed the crown of his head.
He held the pose with a dancer’s grace and magician’s theatrical flair, smiling as if he was on stage in front of a packed theatre and not in a small dirt clearing with less than half a dozen sets of eyes on him. His expression was serene, as though lounging by a pool, breath even and relaxed with not a single sign of tension or difficulty despite the extent of the stretch.
Yuzuriha began to clap and Taiju whooped in disbelief, “That’s incredible! Senku, can you see this? I didn’t even know people could do this!”
Chrome’s arms had fallen in disbelief, head tilting as he tried to understand the mechanics of Gen’s form. “How did you even learn you could do that?”
“The same way you learn most things, I suppose,” Gen hummed, somehow bending his back even further and letting his feet drop to the ground, his upper body popping up to stand up straight as the weight shifted from his forearms to his legs. “Trial and error… though it has been quite a while since I did that particular move. It’s more of an on-the-spot show off as opposed to the true contortions I’d have to get into for my act.”
Taiju clapped the side of his fist into the palm of his other hand, nodding excitedly. “Oh yeah, I remember Senku saying how a lot of those stage tricks are either mirrors or just flexing around things. Like the one where they saw a lady in half!”
Gen laughed softly, “Exactly, though you’ll ruin my image if you start telling all of my secrets, Taiju-chan. In fact, the last trick I did before I was petrified required a fair bit of contorting myself.”
Yuzuriha leaned forward in excitement, “Ooh, which one was it? The sliding boxes one? The shrinking cage?”
“Why the box of swords, of course,” Gen replied with a dramatic toss of his hair, the stage magician persona coming to the forefront, his voice taking on the lilting song-like quality it had when he was putting on a performance. “That one requires a bit less precision and is easy to figure out for skeptics like our dear Senku-chan,” Gen cast a wink at the scientist who hadn’t spoken a word since coming over, jaw suspiciously slack and ears turning a charming shade of red.
Gen filed the expression away and smirked, quickly turning his attention back to Yuzuriha before Senku could snap out of it.
“Because there were always people trying to see through my illusions, I worked to make my hiding spots smaller and smaller which meant that I needed to make myself smaller and smaller." He gave a dramatic pause, subtly adjusting his feet for balance. "Like so.”
He bent backwards this time, threading his arms between his legs to hold his shins, his spine bent effectively in half and peering at them through the space between his knees.
Kohaku cringed and Yuzuriha gasped, eyes wide in amazement as she and Taiju clapped excitedly. Chrome was peering this way and that, rattling off observations and questions as if Gen was some new scientific discovery, but Senku?
Senku stared . His brain was still ticking, but his expression had shifted to something less clinical and much more curious, but not in a data-gathering sort of way. As Gen’s gaze shifted in his direction, he could feel the way his face heated up.
Gen unbent just enough to put his palms on the ground, legs kicking up in a graceful step over, the only sign of exertion being a slight flush to his cheeks, though that could easily be explained by an increase of blood flow to his head from being upside down. He gave a little bow as Yuzuriha and Taiju clapped, retrieving his bundle of clothing from the taller boy.
Chrome was looking contemplative. “Kohaku, do you think you could do that?”
“Maybe with enough stretching,” she replied, though she seemed disinterested in the prospect. “I worked to get flexible enough to dodge attacks, not tie myself into knots.”
Gen smirked as the two began to discuss physiology and body mechanics, Yuzuriha piping in with a bit more information about gymnastics and acrobatics at Kohaku’s mention of Homura, Taiju hanging on her every word as usual. He took a few steps in Senku’s direction and slipped his arms back into his yukata, making no move to retie his obi. “You’re staring, Senku-chan,” he murmured, voice barely loud enough to be heard.
Senku swallowed, his response coming a beat late. “I’m… impressed.”
Gen tilted his head, eyebrow raised and a sly smile curling his mouth. “Hmm? If I knew that was all I had to do to impress you, I would’ve opened with telling you I could fold myself into a suitcase at that ramen stand of yours.”
There was a twitch at the corner of Senku’s mouth, not quite a smirk but not quite nothing either. “A functional spine shouldn’t move like that… but clearly, you weren’t built for function.”
“Oh I was built for function alright,” Gen teased, unable to stop the heat in his voice and gaze as he stared the other man down, “just not the kind you use in public.”
Senku’s breath hitched, almost imperceptibly but to trained eyes like Gen’s it was obvious how his carefully crafted wall of disinterest cracked.
There was a flicker in his eyes, something that could have been intrigue or annoyance, or something more volatile and electrifying. Gen had seen the look before, the way Senku’s breath rose and fell in a steady even tempo just a bit too sharp to be baseline.
Gen leaned just that much closer, disguising the movement by shrugging into his jacket. He saw how Senku swallowed, but before he could speak a strong hand clapped his back.
“That is so cool that you can do stuff like that, Gen! I can't even touch my toes half the time!” Taiju beamed, ignorant to the tension he had broken and Gen resisted the urge to scowl as Senku seemed to snap back to himself.
“Chrome, I have a job for you if you’re done messing around,” the scientist called, pointedly not looking in Gen’s direction, but the mentalist counted the way the back of his neck was still flushed red a win.
—
Senku scowled down at the pile of notes in front of him, hunched over his work top and hair more of a mess than usual from running his hands through it in frustration. The night was quiet, Chrome having turned in for the night nearly an hour prior, leaving him alone to stew in his thoughts.
His thoughts which were absolutely not about Gen’s strong thighs and bendy body and how it would feel to force those legs up and out as his spine arched up to press his front against a warm body over him.
Slamming his palm on the table, Senku growled. “You’re better than this. You’re above this. Hormones are chemicals like any other and you will not be controlled by them.”
He’d known for a while that he was attracted to Gen. The other man was objectively attractive, lithe and graceful, with a smart mouth and scheming mind that drew Senku’s attention like a moth to a flame. He’d had no desire to act on the attraction, simply acknowledging it and pushing it to the back of his mind.
Senku remembered how the boys in school talked about the girls they were attracted to, the discussions of how they were unable to focus on anything but the other person and the effects they had on their dicks. He’d never had that problem, always able to focus on what was more pressing at the moment, casting maybe an idle thought of how pretty Gen’s eyes looked or appreciating the slender circumference of his waist, but nothing more and certainly not enough to distract him.
Yet the image of Gen’s spine bending in a graceful arch, the seemingly effortless way he contorted himself had short-circuited something in Senku’s brain, something primal and not at all scientific.
“Damn it all!” he hissed, burying his face in his hands and slumping down into his chair. He forced himself to breathe deeply, deliberately, in hopes to calm his elevated pulse and redirect the rush of blood that had raced to his groin at the thought.
The flap of fabric that functioned as a door rustled.
Senku didn’t move his hands from his face, didn’t need to. He already knew the familiar pattern of footsteps, soft and bare, the slight drag of fabric and the scent of flowers and wood smoke that clung to Gen like a second skin.
“Something told me you’d still be awake,” the mentalist drawled, voice soft and low in deference of the late hour. “Suppose I should be glad you’re out here where the racket you’re making won’t disturb anyone else.”
Senku clenched his jaw, “Go back to bed, Mentalist, I’m working.”
Gen chuckled at that, the sound closer now, sending shivers down Senku’s back. “Is that what you’re doing?”
He could hear the smile in the words, knew that Gen was cocking his head just so, lips twisted into that maddening half-smirk, eyes glinting with mischief or something far more dangerous.
Senku huffed, “This is so stupid ,” he grumbled, finally letting his hands drop, looking up to find Gen stood with his hip cocked onto the work table, looking down at him. His mouth moved before he could stop it, “Why do you make me so stupid ?”
If Gen was surprised by the admission, he didn’t show it, blinking slowly in a way that fanned his ridiculously long eyelashes over his cheeks. “Why do you make everything so hard?” There was a heat behind the words, a double entendre Senku could have easily ignored.
Instead he took it as the permission he needed.
He stood suddenly, his chair pushing back as he curled his hand into the front of Gen’s yukata and yanked him forward, the other man going willingly, eyes fluttering shut just as Senku crushed their mouths together.
It wasn’t gentle or romantic, nor was it awkward or clumsy as both had expected a first kiss to be. It was teeth and spiking pressure and the sound of something wild giving in at last. Gen slipped off his perch, stumbling back against Senku bearing down on him, fingers tangling in the scientist’s hair in an attempt to angle his head.
When his back bumped into the wall, he melted back, angling his own head to better slot his mouth against Senku’s, the other man’s calloused hands burning a brand against his skin even through the layers he was wearing. He felt Senku’s leg shove between his, forcing them apart to make space for him to get closer, and he shivered, rocking against the pressure.
“Fuck, all I could think about all day was you staring at me,” Gen panted between kisses, fingers delving under the loose collar of Senku’s tunic in search of bare skin.
Senku’s hands had slipped under his jacket, stroking down his sides and palming at the thick muscles of his thighs. For a moment Gen's breath hitched at the thought that he might press him harder against the wall and lift him up, but remembering who he was dealing with the mentalist instead dug his nails into the muscles of Senku's back and slipped his tongue past his lips, grinding their hips together in a way that made the other man hiss into his mouth.
Taking advantage of the brief moment of distraction, Gen shrugged out of his jacket, letting it pool to the floor before leaning back against the wall and luxuriating in the way Senku’s body felt against his, how his rough palms stroked over his hips and stomach under his yukata, stopped by his obi from going higher.
“You and your damn layers,” Senku growled, tugging on the rope holding the obi in place in an uncoordinated huff, refusing to pull back too far from kissing in case Gen came to his senses and put a stop to this.
Gen gave a breathless laugh, the scientist’s uncharacteristic fumbling going straight to his cock as he tried to brute force his way under Gen’s clothes. Senku did eventually pull back just far enough to look down at what he was doing, the scowl on his face a clear sign of his frustration in the moment, and Gen took advantage of his distraction to trace his tongue over the ridge of his ear, biting down gently.
Senku moaned , hips grinding against Gen’s and face falling onto his shoulder as he rutted against him. It was so hot, Gen would’ve done it again if the reaction hadn’t had him throwing his own head back, fingers pulling at the hair at the nape of Senku’s neck and groaning in pleasure.
“Fuck you’re so hard ,” he panted, somehow surprised despite the obvious evidence that Senku was enjoying their fumbling encounter. He used his grip on Senku’s hair to wrench him back up for another kiss, wet and messy as they continued to rock against one another.
Something must’ve clicked as Gen felt the fabric around his waist loosening, the obi falling to the floor around his feet and with a shrug he was able to drop his yukata to his elbows. It didn’t get much further as he was unwilling to release his hold on Senku’s hair and shoulder, but it opened a path for Senku’s fingers to finally slip further up his shirt to palm at his sides and up his chest.
Gen was heavily considering testing the stability of the walls and Senku’s ability to hold him up when the other man’s hand suddenly slid down his back, fingertips digging into the meat of his ass and thigh and lifting.
With years of ballet and acrobatic training, Gen’s leg moved without any real conscious effort. His weight shifted to the other without a thought, Senku’s palm sliding down as his leg went up, knee past his waist and higher still until his calf was up by his ear and Senku’s hand was a comforting warmth on his ankle, pressing his leg against the wall.
“Fuck that’s hot,” Senku whispered, looking down at where Gen’s trousers were clearly tented, hips splayed wide and rocking slightly forward to chase the pressure that had moved away for Senku to better observe.
“You should see it without any clothes on,” Gen teased, finally letting one of his hands drop down, finger tips slowly trailing down his own chest, bumping slightly over the still tied laces of his shirt on its path, ending with a jump of his pelvis as he palmed his cock through his pants.
Whatever tether to his self control Senku had been maintaining snapped and he descended on Gen like a man possessed. Before he could stop himself, Gen moaned, head arched back as Senku sucked and bit at the thin strip skin accessible over his collar, surely leaving dark welts as he ground against him.
The pressure on his ankle was unyielding, keeping him in the standing split even as his other leg shook from the pleasure and tension, every thrust grinding Senku’s clothed erection against his. He felt like he was back in high school, fumbling with another boy in the PE storage shed, too full of raging hormones to even get their clothes off as they rut against each other.
It was exhilarating and if his brain wasn’t currently fogged up by a quickly approaching orgasm, he might’ve laughed at how the thought sounded suspiciously like Senku in his head.
Suddenly Senku stilled against him, body going tense, the grip on his ankle tightening to just this side of painful as his other hand pulled Gen’s hips against his with a firm hold on his ass. He was trembling slightly, teeth latched onto the skin of Gen’s neck just below his jawline, and Gen couldn’t help but groan at the delicious feeling of the other man’s cock pulsing against his.
The realization that he had just made the smartest man alive on the planet cum in his pants sent him over the edge, back arching as far as Senku’s hold and the wall would let him as he shuddered through his own orgasm, hips giving small rocks with each pulse.
He felt like a marionette with his strings cut, muscles lax from his release, body being held up by Senku’s similarly dead weight pinning him to the wall. Senku’s thumb was slowly stroking back and forth against the skin of his ankle, lips brushing against what Gen knew was going to be one hell of a hickey as he struggled to catch his breath.
Nuzzling against Senku’s jaw line, Gen hummed. “Not that I’m not enjoying this, but my leg is starting to fall asleep.”
Senku cursed softly, releasing his grip so Gen could drop his foot back to the floor, bouncing his toes a few times in hopes to redirect blood flow and stop the static tingling having it raised for so long had caused.
He saw out of the corner of his eye the way Senku had begun to panic, the cloud of testosterone clearing and logic starting to take its place.
Well they couldn’t have that, could they?
Senku made a small noise of surprise when Gen kissed him again, far less messy than their previous ones but no less deep or passionate. Pleased when he started to return it, Gen hummed in a way that he hoped communicated his thoughts on what had just happened, hands brushing softly over Senku’s shoulders and neck in a calming manner.
When he pulled back, he was glad to see the panic had abated, Senku looking at him more curious than anything.
“I’ve never done that before.”
“Hmm~?” Gen was more surprised that Senku had made the admission at all than the contents of it. “You would be the type to be good at everything on your first try, wouldn’t you?”
Senku snorted at the teasing tone, rolling his eyes and wincing at what Gen knew from his own situation was the uncomfortable tacky feeling of cooling cum trapped against his skin.
“We should clean up,” the mentalist murmured, fingernails scratching ever so slightly against the base of Senku’s skull. The scientist’s eyes slid shut, shoulders dropping slightly as any remaining tension bled out of him, and Gen tucked that reaction away for future use, leaning forward to whisper in his ear. “Then if you’re up for it, I can show you how I can get both my legs over my head.”
He snickered as Senku shuddered against him, hips close enough that Gen could feel his spent cock give a valiant effort at rising again.
“You’re going to be impossible about this, aren’t you?”
“Impossible? Me? Ever-nay!” Gen teased, going one step further by darting his tongue out to swipe at the reddened ear and purposefully blowing cool air against it as he pulled back, just far enough to see Senku’s expression as he shivered, the glare on his face softened by the flush of his cheeks and how dilated his pupils still were.
Gen took pity on him, pressing a quick kiss to his lips, pleased with how Senku tried to follow when he pulled back. He pushed the scientist back with a gentle press of his finger tips, nudging him in the direction of the wash basin near the back of the lab to clean up.
The process was perfunctory, the best they could manage without heading down to the river or hiking up to the hot springs which neither wanted to do at that hour. Gen had given his trousers a quick scrub, balling them up with his yukata and tying his obi around his jacket in an attempt at decency, noting with a smirk the way Senku’s gaze couldn’t seem to pull away from his bare legs.
If not for the flush that hadn’t fully receded from his cheeks and kiss swollen bruise to his lips, one would never know what Senku had been getting up to just a few minutes previous or that he was now completely bare under the flare of his tunic.
“Suppose you’ll be pulling another all nighter,” Gen mused, keeping his tone light and casual, testing the waters and Senku’s current headspace, biting back a smile at the noncommittal grunt he received in return.
He stepped backward, slow and deliberate, eyes never leaving Senku’s face as the man watched him, the heat in his eyes almost palpable against his skin.
Turning to the door, he lifted the flap out of the way, “Well, don’t work too hard, Senku-chan , I think I’ll head back to the observatory.”
He let the words hang, low and suggestive, pleased with the way Senku reacted at the purr of his name. Stepping into the cool night air, he shivered slightly at the chill to his sweat damp back and crossed the clearing with slow even steps.
As he climbed the ladder he noted Chrome’s absence from his usual sleeping place, smirking at the fortuitous turn of events. Tossing his clothes into a corner to be dealt with later, he set up their bedrolls and left an innocent looking flask of oil within arms reach. Just in case.
Settling on the window ledge next to the telescope, he arranged himself carefully- jacket climbing just that much higher up his thigh, shirt unlaced and neckline gaping to give a tantalizing peek of normally hidden skin, legs draped in such a way to emphasize how long and lithe they were. Casual. Comfortable.
Inviting.
He knew Senku would pretend to hesitate. Pretend to consider and contemplate and calculate.
But Gen also knew the sound he would make when he climbed the ladder and the door opened. How his eyes would darken when they landed on him, lit by pale moonlight just waiting for him.
So he settled in to wait - just long enough to be smug about it.