Work Text:
As far as Gen considered the observatory was the best decision he had ever made and some of his finest work. It had taken a lot of careful planning and behind the scenes machinations to not only figure out how construction would occur without getting any direct input, but how to make it happen in just three days.
Senku’s face when they removed the blindfold had made every bit of it worth it.
The telescope was amateur at best, not even up to par with the most basic of modern day toy telescopes made for children and yet despite that it had become very common to find Senku there on clear nights between projects. Which was how Gen found him that evening, propped on a stool and peering through the eye piece as he made notes on a spare piece of paper.
Gen took a moment to just appreciate the sight, Senku’s pale hair practically glowing in the moonlight, the lack of light pollution making the stars brighter than would have ever been possible pre-petrification. It was times like that where Senku looked closer to his age, shoulders loose and mouth pursed in concentration - a studious teenager and not a chief bearing the responsibility of humanity on his back.
He almost felt bad for interrupting.
Almost.
“Anything interesting up there?”
Senku hummed noncommittally, scratching his pencil over the page a few more lines before looking up with a grin. “Nothing too notable, just everything shifting out of where I’m used to it being.”
“How dare the stars not stay perfectly still and bend to your expectations,” Gen teased, settling down next to Senku with an easy familiarity. “They should know better,”
Snorting, Senku peered back into the eyepiece with a smirk, “Exactly, it’s like they don’t even know how inconvenient this is.”
Gen glanced at the scattered papers at Senku’s feet, recognizing a few from weeks prior as well as a few more recent ones. “You’re telling me, Senku-chan, all my zodiac horoscopes are utterly useless now that they’ve moved around,” he smirked at Senku’s obvious eye roll. “I’m erious-say! With everything so out of whack up there, I might end up dating a Libra,”
“Oh, the horror,”
“Suppose I’ll just have to stick with the Capricorn I picked out,” he nudged him with his shoulder teasingly, pleased with the way Senku’s ears started to turn red.
What they had was new and not quite clear just yet, but Gen was happy regardless. Despite Senku’s bluster and gruff bluntness, he was surprisingly sweet and attentive in his own way. He didn’t need constant attention or reassurance the way previous partners had and was always very clear about his likes and dislikes which eased Gen’s own anxious attachment.
He leaned close, chin hooking over Senku’s shoulder with a purring hum. “So, what are we looking at now?”
Senku shifted slightly to better accommodate the new weight and Gen could feel the heat coming off his cheeks as they flushed. “I’m remapping Altair and Deneb. Ancient civilizations used them for navigation and with the North Star shifted-“
Gen leaned in to kiss him.
It was brief and soft, catching the corner of his mouth and almost innocent except for the way Gen’s hand found his thigh, thumb stroking over the fabric like a promise.
Senku blinked, “What was that for?”
“Felt like it,”
Gen stared back at Senku guilelessly, enjoying the cute pink of his cheeks and the way his brows had knit up just a bit. He looked almost like a confused puppy and Gen resisted the urge to smirk when he caught red eyes dropping to his mouth more than once before Senku turned back to the eyepiece.
“Further south from those is Antares, which you’d recognize as the head on Scorpius. It’s a red super giant and it was theorized it’d go supernova in the next ten thous-“
Gen kissed him again, hitting his target dead on. He lingered, exhaling a sharp laugh through his nose at the noise Senku made - more a surprised gasp than the annoyed grunt he probably intended.
Pulling back, Gen smiled impishly, “Ontinue-cay.”
Senku stared, blinking slowly and absently running his tongue over his lower lip. Gen could see his pupils dilate, though supposed Senku would have attributed it to the dimness of the observatory.
“…then there’s Arcturus, part of the Bootes constellation-“
Gen kissed him again.
“Ursa Major.”
Another kiss, quick and familiar now.
“Kornephoros,” Senku continued more rapidly, body turning away from the telescope and towards Gen.
Gen was seemingly expecting it, his position already adjusted for another kiss.
“Saggitae-“
Kiss.
“Rasalhague-“
Kiss.
“Kaus Austral-“
Gen didn’t even wait for him to finish the last one, hand reaching up to cup his jaw as he kissed Senku properly. Thoroughly. Until Senku’s impromptu lecture dissolved into a startled exhale and he melted into him, hand finding Gen’s thigh for balance and mouth opening so his tongue could slip past Gen’s with a practiced ease.
It didn’t take long for Senku’s lips to wander, mouthing wetly at the corner of Gen’s and down his neck.
“Have I ever told you how hot you are when you’re being smart?” Gen gasped as Senku sank his teeth into the skin just under his jaw, right above the high collar of his shirt.
“Once or twice,” Senku replied, latching on more firmly and alternating between gentle nibbles and more aggressive sucking.
Gen had always been vigilant about his partners not leaving marks to avoid upsetting his manager and make up team, but with Senku he wore every bruise with pride. And a not insignificant amount of arousal.
In the moment Senku took to start undoing the laces on his shirt, Gen clambered into his lap and pulled him into another kiss. Slow and dirty and languid, as if they had all the time in the world, humming when Senku’s hips rolled under him. Fingers carded through platinum hair, fingernails dragging rough lines across his scalp and swallowing the groans it elicited in response, only pulling back long enough to shrug out of his haori before diving back in.
“You and your fuckin’ layers,” Senku growled, yanking on his obi impatiently and latching onto a freshly revealed patch of skin at the base of Gen’s throat, biting down before soothing the sting with his tongue.
Gen choked on a hitched moan, rocking his hips against Senku’s, both of their interest in the current proceedings clear.
Most people saw Senku as someone completely disinterested in sex and romance and, to be fair, just a few months prior Gen would’ve put money on him being some form of asexual leaning heavily towards the “don’t touch me” end of the spectrum. However, he was quite pleased to find that Senku seemed to fall more on the gray-ace demisexual “you have reached relationship level 5 take off your pants” end instead.
Which was very clear when, following a suggestive wave of Gen’s hips, Senku abandoned his attempt to finish undressing him to grab his ass, coaxing him into a steady, rhythmic grind.
“Fuck,” Gen sighed, thighs spreading impossibly wider over Senku’s lap, breath coming in gasping pants and desperate mewls.
Senku pulled back from the necklace of hickies he was leaving, nosing behind the mentalist’s ear and taking the lobe between his teeth. “I was working, you know,”
Gen gave a sharp tug to his hair, head tilting as he wavered between leaning into and pulling away from the sensation at the same time, “And now you’re working me.” He wriggled a bit until his obi slipped to the floor, leaving him in his pants and half open shirt. “Help me get my pants off,”
“Why? You want something?”
“Yeah, your dick in me,” Gen huffed, unfastening the first few catches on Senku’s coat and slipping out of his lap to remove his pants.
Senku barely had enough time to shrug his arms out of his sleeves before Gen was back in his lap, shirt still half undone but bare from the waist down, arms looping around Senku’s neck and mouth demanding. Senku would have laughed at Gen’s eagerness if not for just how good the pressure against his erection felt, even through the fabric still spread over his lap.
“There’s no way we’re not going to eat shit if we try to fuck here,” Senku muttered against Gen’s lips, already struggling to maintain his balance on the stool against the mentalist’s onslaught. “We need to set up the bedrolls or you’re getting it on the floor,”
“Way ahead of you, darling,” Gen cooed, tongue flicking out to lick the shell of Senku’s ear before nipping at it teasingly but making no other move to stand back up.
Senku was usually fairly logical and realistic, but in that moment he genuinely considered if he’d be able to stand while lifting Gen along with him just so he wouldn't have to let him go. Fortunately for both of them, he knew better than to test it.
“You’re gonna need to let me up,” Senku grunted, immediately undermining his statement by palming at Gen’s ass and dragging him more firmly against him.
It took several attempts and a few false starts but Gen finally moved to stand, dragging Senku up with him so as not to break their current kiss. Stumbling over their own feet and Senku’s brilliant idea to just let his coat fall to the ground, they fumbled their way to the bedrolls, practically collapsing into a heap on top of them.
“In me, now,” Gen growled, pawing at Senku’s erection through his primitive underwear.
Hissing through his teeth, Senku reached for the vial of lube Gen had left within easy reach, “If you wanted it so bad you could’ve said something,”
“Wouldn’t have to if someone didn’t sleep in the lab for over a week straight,” Gen hooked a leg around Senku’s waist, forcing his hips forward to grind against him.
Senku cursed but otherwise had no retort, using his free hand to press Gen’s other leg flat to the floor as he attempted to shuffle backwards for more room. “Well if you want it you need to hold still,”
“Or else wh-nnng…”
Gen’s back arched as Senku slid a finger in, pumping his wrist a few times before zeroing in on his prostate with the aim of someone who knew the landscape intimately. When no second finger was forthcoming, Gen whined low in the back of his throat.
“Hmm? What was that?”
“Senku-chan, please…”
Senku slid the second finger in, smirking at the way Gen’s thigh tensed under his hand. “Please what?”
Gen flushed, head rolling against the pillow and hips rocking as much as they could in his current position. He gave another keen, twisting in an attempt to direct Senku back to his prostate, groaning in frustration when it didn’t work.
“You’ll have to tell me what you want if you want to get it.”
“You’re such a dick,” Gen moaned, Senku ghosting over his prostate for a moment before pulling his thrusts back, scissoring him open.
“You had no problem saying it before,” Senku practically purred, reveling in Gen’s descent into desperation, his own erection rocking against the other man’s inner thigh in a slow metronome. When Gen bit his lower lip to stifle another groan, Senku curled his fingers in a come hither motion that he knew always drove him wild.
“Oh fuck,” Gen practically sobbed, muscles tensing like a live current had raced through him. “Hnnngg…”
“C’mon, Mentalist,” Senku smirked, giving a deeper thrust of his fingers and relishing in the way Gen’s cock jumped between them. “Just tell me what you want.”
Gen trembled, head thrown back wantonly and voice pitching up. “Fuck me,” he demanded, legs spreading impossibly wider and the hand in Senku’s hair yanking him down for messy kiss. “If you don’t get in me in the next ten seconds- ah, ah-“
Suddenly there was a slick hand on the back of his thigh, forcing his leg to fold up at the hip, and he barely had a moment to register the sudden emptiness before something thicker and firmer was pressing against his entrance.
Automatically, Senku captured his mouth, swallowing the lewd noises Gen was making as he bottomed out. Back arching, nails scrabbling up his back and shoulders, breath coming in desperate punches, Gen writhed against him as Senku gave a few tentative thrusts.
“This what you wanted?” He muttered through a gasping laugh, rocking more firmly in and grinning at the way Gen keened in response. Ducking his head, he mouthed at Gen’s neck, lips latching and tongue worrying the skin as he started to pick up the pace.
It took only a few moments before Senku found the right angle, the way Gen gasped his name every few thrusts between moans of pleasure was debauched.
Senku was fairly sure he could’ve come just from the sounds alone.
“Fuck, fuck, right there,” Gen hissed, groping aimlessly at whatever parts of Senku he could reach - his chest, his shoulders, his neck. His fingers laced through sweaty hair, seemingly unable to decide if he wanted to kiss Senku or just needed something to hold onto, and Senku took the opportunity to sink his teeth into the meat of Gen’s shoulder where it met his throat and start working on another mark.
Gen squirmed against him with an adorably trembling whine, and Senku reached down between them to find his soaked cock, fisting it in time with the pounding thrusts he aimed directly at his sweet spot.
“‘M gonna cum, keep- keep, oh fucknnn…” Gen quaked around him, voice getting louder and sweeter before he came over Senku’s fingers in long, needy stripes. The sound of his name on Gen’s lips was practically a sonnet as Senku fucked him through his orgasm, his channel tight and hot around every aching inch of him.
He was already hovering over the edge when shaking hands cupped his jaw, pulling him into a kiss far too sweet for the filthy mess between them. All it took was a brush of Gen’s tongue against his lower lip and Senku was gone, hips rutting forward as he spilled as deep as he could.
Before he could pull out, Gen’s legs locked around him, holding him in place as the lingering aftershocks coursed through. Every few seconds Gen’s hips gave a little rock, whining in over-sensitivity as Senku nibbled at his neck and collar bone.
Senku could feel himself softening inside, pressing one last open mouthed kiss to what he knew was going to be a particularly livid mark come morning. He wouldn’t admit it out loud, but in the afterglow he could acknowledge that going more than a week without this - the ladder of their fingers laced together, the sound of Gen’s voice lost to pleasure, the fit of their bodies - was becoming more and more difficult as time went on.
Luckily Gen had no such compunction.
“Next time you spend a week in the lab, I’m making you fuck me on your work table.”