Work Text:
It was an early night after dinner in the observatory. Senku decided to work a little more, Tsukasa is in the freezer so they need a plan. And as if on que, the door to the observatory opened following with Gen’s greet. He brings some tea for them to accompany them throughout the night like usual.
Gen said it’s jasmine that he gathered this morning. He said something like it had a soothing smell so he took double the amount Senku had. Senku drinks the tea as he continues his calculation. It does have a soothing jasmine smell. It has a hint of sweetness in it. Probably Gen forgot to make it the unsweetened one he usually has.
After a couple of nights they spent oversleeping thinking about strategy and all, Gen built up habits to bring tea and prepare futon. He said one night something like if we’re gonna fall asleep in the end, might as well sleep in bed. Which is, fair enough.
A few minutes later, Senku was lost in his research. Then his concentration was broken by a sudden heat rising. It’s getting hot. But it’s weird because the observatory was left open and it’s not summer yet. Just then Senku feels the heat focused on his lower body, with the uncommon feeling in his stomach. Senku’s mind instantly runs into possibilities about what will happen to his body. When he realizes, take the mug to smell and taste the remaining tea.
“Mentalist, what did you put in the tea?”
“Did you feel what I feel, Senku-chan?” Senku turned around and found Gen already taking off his haori, sitting on the futon, looking down. His face was so red, and it’s visible that he’s sweating. Senku probably froze too long, because Gen started to ramble. “I swear it was jasmine, it’s the same smell, appearance, color.” Gen brushes his lips; it looks like there’s a buildup of saliva, too. Senku didn’t realise that Gen has pretty plum lips that look tasty. What? “Fuck. I dried it and turned it into powder, which could make a high concentration of whatever it is.”
“It’s probably an aphrodisiac.”
“Damn it. Sorry, Senku-chan, I didn’t mean to. I’m gonna take care of it.” Gen is shaking. He tries to stand up, but immediately collapses to a sitting position again. Senku in reflex holds Gen’s arm.
“You okay? You take twice the dose than me.” Gen is visibly heaved looking up to Senku. “Aphrodiastic can induce muscle relaxation. Seems like your leg gave up.” They both sit too close with each other. They practically share oxygen at this point. Gen’s half lidded eyes had gone glossy.
“Senku-chan.” Gen's breathy voice made Senku’s situation worse. “Don’t look at me like that.”
“Like what?” His voice was a few octaves lower than he let out. Senku’s brain definitely started to shut down because he didn’t register the response beforehand.
“Like I’m a prey.” Did he really look like that? Or maybe Gen really is his prey? What the fuck he’s thinking. “I’m serious, Senku-chan! Let me handle this, and you can handle yours!” Gen shoved Senku face away and turned his body so he sat with his back facing Senku.
“Alright, I’ll talk to Chrome first, I’m not gonna risk being interrogated tomorrow.” Before getting a response, Senku gets down to the storage room below and sees Chrome still awake. The boner between his legs makes it uncomfortable to climb down. He makes sure the clothes are baggy enough to not let it be visible. Glad he still had some will power and probably adrenaline to deflect some of the symptoms. Chrome’s still restocking the rocks he got this morning.
After Senku sent Chrome to sleep with Kaseki and make sure he had everything he needed so he didn’t come back for this night –with additional promises Senku had made so he didn’t ask more–, Senku came back to the observatory, and found Gen with pants off and the top opened without the lace so it’s like a vest. Senku notices that his skin looks milky under the moonlight with additional redness on. Gen apparently had started caressing his shaft with his eyes closed.
Senku turns his attention to the observatory window. Ignoring his horny feeling building up. He’s not even know there is a possibility that he is attracted to men or even people in general. He had watched porn, he’s a curious teenager after all. It helps him do the business. Then he got intrigued over the biology of sex so he did research for his general knowledge in the future. Not in his knowing that he would use it on a man, especially his friend. Anyway, knowledge is knowledge, it’s useful in some kind of way. If it means helping his friend's business then fine by him.
Senku closing the window. Light up the oil lamp. What else did he need? Thinking practical things does ease the heat down there. He emptied both mugs with the tea. He’s not risking accidently taking it. Gen probably needs some kind of lubricant. Sunflower oil will do. And water when he remembered how much sweating he was. Senku sits back to back with Gen. And places two jars beside them. “Here, some oil and water.”
“Thank you, Senku-chan, you don’t have to.” Forget about easing the heat, It got back again ten billion percent worse the moment he heard Gen’s breathy voice with a slight whining. Gen should be banned calling him in that manner forever. At the very least not if he’s working.
“Somebody has to take care of you, and I know damn well you don't want anyone to know.”
Gen scoff “Damn right.”
With his peripheral view, he can see Gen take some of the oil from the jar. With the silent night, Senku heard everything. And it is bad. Not Chrome’s bad. But a literal bad. Like, He’s fucked up.
Senku can hear Gen’s heavy breath. The rubbing. The slick sound the oil made. Gen’s choked sound and then Gen’s little whining. That indicates that he's not satisfied at all. The sound is definitely a devil temptation for Senku. His shaft was hard to the point it hurt.
As he succumbs to the temptation, he takes some of the oil and starts stroking. He bit his lower lip hard to stop the relieved moan out. He wants to end it fast, but at the same time he wants to enjoy it. What a useless dilemma he’s having. As it gets hotter, he’s undressed quickly. He doesn't want the heat to be abandoned too long. The ruffle sounds it makes could indicate that Senku ran out of patience. Because he is. Senku’s hand went back to his shaft, eager to chase the pleasure. He played with the head where it’s the most sensitive. He couldn’t help but let out a soft moan.
When he thought it couldn't get any hotter, Senku heard a yelp followed by a moan. And Senku did not miss to know that Gen had picked up the pace. Senku slowed down his pace to hear Gen’s now loud moan. He’s moaning and whining like he’s forgotten Senku’s in the same room. Senku imagined Gen’s desperate red face and how it would suit his cute whining voice. Senku would love to see that under his arm. Senku closes his eyes in an attempt to distract himself. But oh boy how wrong he is. The image becomes clearer in his head.
Fuck, this is the worst. Fantasizing your own friend sexually desperate would be the most weird thing I’ve done. Senku didn’t realise he was grunting while he’s dripping pre cum. Not long after, by the frantic movement and high pitch moan, Gen could be in his orgasm. When there’s no movement from Gen, Senku catching his breath, apparently he had been drooling the entire time. Does that mean Gen’s done now that he got his release? That’s a bummer. He had to take care of himself without Gen’s voice.
“Senku-chan” Senku opened his eyes to find Gen half sitting in front of him, naked with a flushed face. Senku stopped everything and watched Gen sit on his lap with wide eyes. “I have a favor.” Gen wiggling on his lap and looks troubled and hesitant. “I want to be fucked. It’s perfectly fine if you don't want to touch me, but please let me use your cock.”
Senku gulped as he heard that. And blinking the second time in shock and disbelief. You want what?! Can he just do that? To his friends? To his undoubtedly ravishing friend? People can say that he’s not attracted to anything but science, but he can see if things are objectively beautiful. He’s not blind.
“Please Senku-chan, I’m begging you.” Senku observed Gen. He’s sweating and his cock wet, possibly he just cum from his masturbation before. “My finger is not enough, a– and your voice is triggering me, I can’t hold it anymore.” Did he just confess that he plays with his ass because of the sounds he makes? Apparently Senku’s voice has the same effect as Gen’s. This aphrodisiac is really dangerous for his sanity.
Senku gulp for the second time. “Do whatever you want.” The response came out surprisingly easy. Senku cannot really refuse it when he would benefit from it too.
“I owe you one, Senku-chan.” There’s a relief on Gen’s face. He poured some oil on his hand and started fingering himself. Gen is a whining mess. Flushed face. Half lidded glossy eyes. The mouth opened. Senku can see his little tongue. And a drool trace on the side mouth. Damn he looks so desperate and it looks so hot. His cock twitching from the sight.
When Gen put Senku’s cock in, he thought he saw heaven for a second. Gen apparently didn’t wait any longer and started with fast pacing already.
“Ah, fuck! Yes!” Gen arching while grabbing Senku’s thigh for better movement. Gen’s inside is so warm and tight. And with the sensitive cock he had before, the feeling was so intense, Senku couldn’t care less about moaning and grunting anymore. He grabs the futon tightly, trying to not cum easily.
“Shit, it’s not enough, I need more.” Gen’s pace is only getting faster. Senku gets even hornier –if that even possible– at the sight in front of him. Gen stroking his own cock. That leads to his hazy eyes almost looking like a mindless face only chasing pleasure from his toys. He wants to know what expression Gen would make if he’s in orgasm. What if he’s covered in bites. What if he’s covered in cum. What if he’s writhing in pleasure because of him. Senku gulps his build up saliva at the thought of it.
“Fuck, Mentalist! Can I touch you?” Senku’s mind is blank.
“Yes, yes please Senku-chan please, I ne–Ahh.” Senku did not waste any time, grabbing Gen’s waist and shoved him hard. Then to fulfill what he wants, he bites Gen’s shoulder. Gen responded by grabbing Senku’s back hair. Senku savour the taste with kisses, licks, and sucking. Senku’s mind had long gone and let his instinct take over.
Senku’s bites and sucking on different surfaces in front of him are not stopping even if Gen keeps bouncing on his lap while arching. Not even when his hand grasps Gen’s ass tightly that would definitely bruise. Not even when there are stings of scratches on his back. Not even when the cock that brushes between their stomach gets more and more wet.
“Senk– Com- Coming! Ah” Gen’s pace became irregular when he began to tremble. His insides become tighter as if he’s milking Senku’s cock.
“Oh Fuck, you’re so tight!” Senku taking over pounding Gen. Senku refuses to close his eyes to watch Gen in pure bliss as he’s cumming, wetting their stomach. Gen’s eyes rolled back. Trembling. Back arching. Skin flushed highlighting the marks on it. Mouths open, babbling Senku’s name. Senku decides that’s a sight worth remembering with his eidetic memory.
Senku keeps the pace as he’s let out his load inside Gen. Senku let out loud groan-moan. Until everything is out and he slumps his body toward Gen with his head on his shoulder. Senku could feel hot breath on his neck as well. Senku let himself relax. He still felt that the heat hasn’t gone completely, but it’s definitely toned down. Probably he just needs one cum to let the aphrodisiac out of his system.
“I don’t intend to ruin this relaxing moment, but I don’t think we’ve done.” Gen’s heavy breathing almost covered the word.
“Yeah, I feel it too.” In a moment of haziness, Senku’s hands tracing Gen’s skin that could be reached while humming. Thigh, waist, back, ass. It’s so smooth. That gives shudders from the other. “Just give me a sec.”
“Don’t know that you become touchy in bed, Senku-chan.”
“Don’t know it either, probably because I gave up thinking a while ago.” Senku resumed his desire to licking and sucking toward Gen’s neck.
“Mmhh, did I just find something that can make THE Senku-chan not think?” said Gen teasingly. That leaves a grumble of disapproval from Senku.
“Don’t you dare give me that tea ever again. Or any aphrodisiac matter.” Senku pinched Gen’s ass lightly for warning.
“Ow, I don’t think I want to deal with bitey Senku-chan again.”
With a burning competitiveness, Senku laid Gen on the futon then stepped back to look Gen from above. He half-pull his cock out. That makes Gen let out a soft whine.
In an act of teasing, Senku pressed an area on Gen’s stomach while he pounded back where the prostate should be. That got an arch Gen with a chocked followed with a moan. Well that’s beginner luck.
When Gen came back to his senses from the sudden pleasure, he had glossy eyes and definitely a horny face on. Senku licks back his own drool. His hand on Gen’s thigh grasped tightly as the sight was presented. The dented part makes his thigh look so soft and squishy.
For better looking, Senku’s other hand runs his hair back –the moisture from his sweat must be depressing his hair. Gen could be seen breathing heavily. Senku admits in his head that Gen’s under him is better looking than before.
“Your inside says otherwise.” There is a sense of pride lingering. Senku could feel the inside pulsing more than before. It gives a nice feeling. Senku wondered what variable that triggered it.
“Ah, that's the aphrodisiac thing working.”
“Sure, but you definitely would like me to be able to think while taking care of you.” Senku pressed the same area again.
“Ohh-mmh, should I, Senku-chan?”
Senku cannot help but smirk. “Is that a challenge?”
“I don’t know, what do you think?” Said Gen while tracing his soft long fingers on Senku’s arm and shoulder. Senku knows the Mentalist intentionally provokes him. But knowing it doesn’t mean he’s immune to it.
“Heh, don’t play with me, Mentalist.” Senku let his cock out and earned a protest whine from the other but he ignored it. “Turn over.” the authority tone somehow comes out naturally.
As Gen lay on his stomach, Senku takes the rudimentary pillow and puts it under Gen’s pelvis, essentially rubbing his cock while his bottom is in the air. “Here, a pillow for you to grip or bite.”
Senku received a pout when he threw the pillow to Gen’s face. He smirks at that before he starts biting Gen’s ass. Senku decided to insert his three fingers to play with his prostate while licking the cock’s base. There’s a muffled moan in response.
If Senku’s calculation was right, Gen needs two cum while he himself could only last for one cum more. In conclusion, Gen had to cum from a foreplay first, or at least sensitive enough to an immediate cum from penetration. Then Senku can give his all in the end. Well this position is exactly for that purpose. It would make double stimulation easier. That leaves out the foreplay. Senku would gladly do it.
Senku hasn't laid his mouth on other people before, let alone man’s private parts. Yet Senku was curious enough to do it. His fingers go in and out pretty easily with how wet the hole becomes. Bonus points with the movement have made friction on Gen’s cock.
Senku secretly loves the sight of his semen dripping out of the rim. So, Senku licking and lightly biting around the rim. He practically tastes himself. A bit salty, not really his liking, but the shudder moan response definitely is. He’s considered enough to not make a mark there. It would be literally a pain in the ass to sit on. But, the thigh should be bearable.
Senku makes sure his fingers brush around the prostate and only occasionally pound it hard, to give Gen longing and anticipation. In short, Senku wants Gen to be needy. And his strategy has success when there is a desperate whine as Gen’s ass chases pleasure from the pillow and his fingers.
“Senku-chan, please.” that breathy whine is butter to Senku’s ears. He takes back the banned word. Gen can use that everytime he wants. Yes, yes even while he’s working. That would be a distraction, but a good one.
“Please what?” Senku tries to ease –or maybe make it worse– by licking and kissing his back while using the other hands to tracing his waist and thigh.
“Please, I need it.” Senku continues to tease the prostate. And now the licking has landed on the shoulder blade. There’s something Senku wants to try.
“What do you need, baby?”
“Mmhhaahh.” Gen’s body becomes trembling and the inside tightens to the point the fingers are hard to move.
“So, someone likes pet names.” Senku couldn’t help but tease him. Well, a pet name is some kind of foreplay anyway.
“Umhh, stop teasing, Senku-chan.” Senku can see how tight Gen’s grip is on the pillow.
“Mm, so what should I do for you, baby? What do you need?” Senku’s voice lowered a few octaves. Yes, Senku knows what he’s doing.
“Mmhh.” Gen turns his head so he can face Senku with the lewdest and broken expression Senku had seen. Which is not much reverence but nonetheless ravishing in his eyes. “Please, I need your cock in me, Senku-chan.” Senku would easily get used to the pride in his chest.
“Whatever you want, baby.” Senku gave a lick on the shoulder before he let his finger out. Without wasting any more time, Senku aims for Gen’s prostate hard.
Senku makes sure to enjoy the feeling and the sight under him. He bent, then his hand pressing Gen’s back so every thrust was gonna hit the same place again and again. Beside that, Senku had to make sure Gen’s cock got the friction too. Senku needs Gen to cum first.
“Ahh, yes, yes, so good! Ohh.” Gen’s a moan mess with his back arching. To be honest, Senku wants to bite every millimeter square on that surface. Clouded by lust, Senku bent over to lick and bite Gen’s neck. That leaves a yelp and a mark. Senku cannot ignore the sudden tightening feeling around his shaft.
“Ohh, so good to me, baby.” Senku decided to abuse the prostate again and again. Making sure that Gen would get what he deserves after several neediness.
“Wai- ahh, Senk- ohh, if you keep- ahhh, doing that hahh I’ll- I’ll Ah! Fuck so good!” His whole body tense while arching. Senku can see a glimpse of Gen’s wrecked face with drool and tears.
“Let it out, baby.” You have to cum now, Mentalist, It felt too good.
“But- Oh no, hahhh, shit, ahh, Come- coming! Ahhh!” Senku gives a couple of thrust so Gen could let it all out. As Gen finally slumped and relaxed, Senku let out his cock so he’s not tempted to chase his own pleasure. If Senku grabbed the base of his own cock, Gen wouldn’t know that.
In between their heavy breathing, Senku marvels at Gen's glossy back. “Still needs to cum, Mentalist?” Gen’s only response is nodding. “How many?” now only one nod. Good, I can’t afford more than one, and I definitely had a big ego.
“Ppfff.”
“I just said it out loud, heh?”
“Yeah.”
“Turn over and get this over with.” Gen turns over and reveals the violated pillow. Gen looks a mess. Cum on his stomach, bite mark, glossy skin, flushed neck and chest.
Too bad he hides his face under his hand, but at least he got his neck in full display. His dick twitching cutely, and don't let him start with his restless rim he got.
“Like what you see?” Senku decided not to respond by biting Gen’s inner thigh. “Ack, can you stop with the biting?” Senku chose to ignore him.
“Shut up.” Senku put his cock in and began to thrust slowly and shallowly. Different than before, he’s thrusting just deep enough before brushing the prostate. That not much got a moan from Gen, only heavy breathing and occasional whining when brushing the prostate lightly. But it’s good for the long run.
In the meantime Senku would gladly taste Gen. He started with his neck. He made sure he made a hickie, it would be covered with his clothes anyway. Then his shoulders then down to his chest.
His chest area was covered with his mark. Senku didn’t realise how much he had bitten before, but the past Senku had left a specific part alone. And now he would take it.
Senku licks Gen’s nipple hesitatively while looking up at Gen’s face searching for reaction. Now he and Gen are much sober, he’s getting nervous. Gen looking back at Senku with hazy but curious eyes. He’s not hating it. Gen’s hand softly grabs Senku’s hair. That’s his cue to start playing it.
Senku licking and sucking it while his other hand caresses the other. There’s a shuddered breath. That makes Senku confident enough to bite the nipple teasingly. Senku could feel Gen’s arching and rolling his hips in an effort to chase his pleasure. As Senku kept teasing, the hand on his hair became grabby but not pulling out.
“Ack! Mmhh” Senku decided to end it with a bite and the last lick before his mouth came back to Gen’s neck. Gen tilted his head so Senku would get full access. So Senku takes the opportunity to tease him.
“Do you like it, baby?” Senku would definitely get used with the pet name. Especially when Gen is whining because of it. He really is a baby.
“Mmhh, I would like it more if you start pounding me hard, Senku-chan.”
Senku let out an amused scoff. “Alright.” Senku grabbed Gen’s thigh and started to thrust deeper than before. That makes Gen’s arching. Senku decided to move it slowly but hard and steady. Gen is moaning while his body is squirming.
Senku could feel the tense of Gen’s inside. The slow pace enables him to feel pleasure in a bit more detail. He let out moans as he savored it while he’s nibbling Gen’s neck and ears. “Ahh, fuck, so good.”
Senku didn’t know that going slow and deep would be this good. He thought going fast makes a lot of friction and would create much more pleasure. But he guesses that’s not the point when the inside is doing the job already.
Senku lost in his pleasure until the grip on his back tightened and he heard a blabbered mess from the man under him. “Hmmhh, what is it baby?”
“Hahh, please Senku-chan, please so good, more please, mhhh.” Hearing that Senku couldn’t help but increase the pace. Gen’s inside gets tighter than before. It was pulsing so it gave Senku the sensation that he’s being milked.
“Ohhh, so good to me, baby, ahh.” Gen’s under him become frantically squirming. Senku had to harshly pinned him down with the hand on his thigh. Senku couldn’t care less if his grip would leave a bruise.
Senku takes a distance to see Gen’s face. And shit, it is so lewd. Looks like Gen’s ability to think has long gone. That flushed face and chest with drool and tears on. Parted mouth to moans and half lidded and partially rolled eyes.
“Ughhh, Senk- aahh, fuck, please faste- Aah!” At this point, Senku only focused on pleasuring himself. And still managing to not cumming first. He had to have credit for that.
Adrenaline makes Senku ignore the ache of his leg and back. As Senku keeps the pace fast, he can feel Gen’s inside massaging him. It felt heavenly. And Senku knows if it keeps going this way, he could end first.
“Arghhh, cum for me baby, you’re so tight for me, so good, ohh.” Senku managed to lick Gen’s ears, neck, and shoulder. He did that to ease his pleasure by distracting. While his hand pressed Gen’s stomach where the prostate would be. Senku’s pride wants Gen to cum from his cock only. He refuses to touch Gen’s cock.
“Ahhh, Co- coming!” Gen’s body shuddered frantically before the white liquid came out from Gen’s cock with a high pitch moan.
Senku finally could let himself come inside Gen with a long low groan. Senku let a few slow thrushes again to empty himself before he took it out and collapsed on top of Gen with heavy breathing. He fortunately was not squishing Gen with his weight cause his hand still managed.
Their faces are so close they are practically sharing oxygen. Gen face is what he can call pure bliss. The pride in his stomach lingering. He swore he was so close to blacking out because of lack of oxygen. Or maybe out of pleasure.
When he finally catches up, he lets his dick out and lies spread out beside Gen. They lied there for a few minutes, focused on breathing.
“We have to burn this futon.”
“Agree. We have to have a warm bath.”
“Agree.”
But both of them haven’t moved at all.
“My leg hurts.”
“My throat hurts.”
They look at each other. It’s only blank and exhausted on their faces.
“We really need to burn this, Senku-chan. No amount of washing is gonna save this. Not in the stone age.”
“And we need a warm bath. Your inside needs to be cleaned and I want to ease sore muscles.”
“Tonight?”
“Tonight, while there is still adrenaline left. And I haven’t felt sleepy. Fortunately we start when the night is still early.” Senku decided to be the first one to sit up and put on some of his clothes.
“Help me?” Gen makes a pouty face. Well he did get the most impact between them.
“Fine, wait okay.” Senku takes Gen’s used haori and pants beside him. “At least wear this first, while I prepare for things.”
“Thank you, Senku-chan. You’re the best.” While Gen puts his clothes on rather slowly, Senku walks around the observatory to take some of the essentials. Basket, their clean spare clothes, drying clothes, soap, and oil lamp for lighting. That should be all.
When he came back to Gen, the man had put on as much as he could but still lay down. Gen made a pouty face and reached both of his hands up. He really is a baby, Senku thought fondly.
“To give you warning, I can’t carry your whole weight, so you have to at least try to walk.” Senku put the basket down then crouched to reach Gen, giving him a lift in a hug manner.
“Yeah, I know, I’ll try, but I still need the support.” They walk slowly to the entrance. Senku climbs down first so if things happen, Senku can catch Gen.
And it did happen, fortunately it’s on the last step before ground. Senku managed to catch him by the waist. What a helpless baby.
Senku supports Gen while they’re walking to the onsen. Gen was the one that carried the basket because both of Senku’s arms were occupied. The hot spring is pretty far, but it’s gonna be worth it.
When they finally arrived, Senku let Gen sit on one of the dry rocks. Tempted with the warmth of it, Senku immediately took his clothes off.
“Really Senku-chan? In front of me?”
“What? We did a lot more embarrassing things tonight. Looking at your naked body is hardly embarrassing now.”
“Well you’re not wrong, but still.” Gen took off his clothes slowly.
The hot spring they decide to use has a running water system. That makes the water change the entire time. So they don’t have to worry about dirtying the water.
Senku helps Gen so they can go to the onsen together. The warm water let out a big sigh from both of them. It's a pretty shallow one. The water level only on their chest when they sit under.
Senku got much more relaxed and wanted to lean on. He can feel the rock behind him with his hand, then the rock grazes Senku’s back.
“ACK! Fuc- bllrrgh” the grazes sting his back a lot and it caught him off guard. Resulting him to step forward out of reflex. Then the slippery rock under the water plus his weak leg makes him fall under the water.
“What the fuck?! Are you okay?” Senku can hear Gen beside him when he resurfaces with a gasp. He let out a couple of coughs.
“Yeah I’m okay now.”
“What happened?! You suddenly fell. That’s kind of funny, not gonna lie.” Senku could see Gen’s worried eyes but a twitch on his mouth.
Senku let out a glare toward the Mentalist before answering. “It’s my back, grazing the rock.”
“Wait, let me see.” Senku could see the exact moment Gen realized something. He actually didn’t want him to see. By the feel of pulsing on his back, it’s pretty bad.
“It’s okay! I just caught off guard.” He shrugged it off.
“Well I still wanna see.” Gen turns his shoulder to make his back facing him. Senku can hear the loud gasp behind him. “Was that me doing?!” Senku can feel a hand cautiously tracing it. His body shuddered against his will.
“Who else I spent the night with?” Senku takes Gen’s hand off so he can properly lay his head and back against the rock slowly this time.
“Ah, I’m sorry, Senku-chan, I didn’t realise.” He can see guilt on Gen’s face.
“Don’t be.” Senku lay his gaze toward Gen’s neck, shoulder, and chest. “I did plenty to you too.” Now Gen looks at his own chest with a blushing face. “Just called it even.” He can see Gen’s nod before he closes his eyes to relax. Now that he’s completely sober, what had happened hit him differently. “I’m sorry, Gen, that must be hurt, that much too.” He remembered Gen’s chest and thought that it was overkill. What is he? An animal? “I should have controlled myself.”
Senku heard Gen mumble something but he couldn't catch up. He opens his eyes and sees Gen turn his head so Senku couldn’t see his face. But he still can see the red on his cheek and neck.
“What?”
“I said, it was good.”
“Oh.” Senku couldn’t help but feel embarrassed at the moment. “It was good for me too.” Gen turned his head so their eyes met. Gen suddenly smiled shyly. Now it's Senku's turn to turn his head. He can feel his ears getting hotter. The mentalist must have catched that.
Senku felt like an idiot to feel embarrassed just by saying it. It’s only objectively good, it’s essentially a sex with drugs, of course it’s good. Why is he overthinking it?
“Should we use soap on our wounds to prevent infection?” Right, those are wounds. We can’t afford an infection in the stone age.
“Yeah, yeah we should.” Senku gets up to sit properly.
“Let me rub your back, Senku-chan.” Gen’s voice is much softer than what Senku usually hears.
Senku wanted to protest, but seeing Gen’s determined face, he stopped himself and nodded. So here, on the rock, out of the onsen, Gen rubbing his back cautiously. It sting a lot but he managed with a bit of shudder and groan. After Gen’s done rinsing him, Senku had to ask him back.
“Now let me do yours, Mentalist.” Before he heard any protest, he turned around to snatch the soap and sat close to Gen. He rubbed Gen’s chest, shoulder, and neck. It received some hisses from the other. Senku tries to ease the pain with his other hand –without the soap– rubbing Gen’s thigh. Senku rinsed the soap out of him before he moved on to the lower part.
“Open your leg.”
“W-what?”
“I was biting you down there too. Now spread your legs.” Senku’s hand gently spread open Gen’s leg. “Get down a little, Memtalist.” Senku pushed his stomach a little to reveal Gen’s marks on his inner thigh, a couple of bruises, and his puffy rim. Senku started rubbing the marks and around the rim. After that, Senku rinsed it.
“Okay, done.” When Senku lifts his head he sees Gen’s flushed face with parted lips, diverted his gaze from Senku. He just noticed Gen’s heaved chest. From that information, his gaze goes down to check something. He’s half hard.
Senku started to think Gen’s some kind of a masochist. Well that makes himself some kind of a sadist. So it’s fair in his head.
“Seriously, Mentalist?” Senku decides to tease him.
“I can’t help it, okay!”
“Have you cleaned your inside?”
“Um, I haven't yet.”
“Alright, perfect.” Last round it is.
“Wha- hahh!” Senku strokes Gen’s cock while his tongue licks the rim. A hand lands on Senku’s head trying to stop with not much effort. When it’s slick enough, he starts fingering Gen with two fingers already. He scissored the rim open so the water can go in to clean up. The writhing body is a bonus point.
As he continues cleaning up, he decides to tease the man a little bit. Senku licks Gen’s base while he uses three fingers to search the prostate.
A hand grip the back of his head gives him more confidence. So Senku tried to put Gen’s dick inside his mouth. He did it cautiously so his teeth wouldn’t graze it. This whole night was really like a delightful experiment for Senku.
As he licked Gen’s cock inside of his mouth, he brushed the prostate too. That gets a jolt from Gen and the hand on his head pushing him down makes him choked. Triggering him to make a swallow movement and increasing his saliva.
All that makes Senku sucking Gen’s cock even more. Senku blinked tears in his eyes. It caught him off guard. But he’s an adaptive person. So he tries to keep his level headed and resuming his fingering to aim at the prostate and sucking up.
“Ahhh, fuck.” Before Senku understands what happened, the hand is already pulling him out. The next thing Senku realizes is the white liquid on his face. “Senku-chan you’re crazy!” Senku licking his own lips with the sperm on it. Salty, again, not his liking, but Gen's expression definitely is. “Oh, fuck, Senku-chan.” Gen cleaning up Senku’s face with the spring water.
Senku let out a cough before talking. “I thought I would die.”
“Did I push you?”
“I think yeah.”
“Ah, sorry. Wait, I should be mad, what are you thinking about suddenly giving me a blow job when you are fingering me!”
“What? I just want to make it end fast.” Senku answered matter of factly while scratching his ears.
“I didn’t used to this! I could injure you like that or worse!”
“Wait, is this your first?! All night we did?!” Gen didn't say anything, but his face flushed really red. “No way! You’re like, what? Four years older than me before the petrification happened! And you are an entertainer! The chance for you to still be a virgin is too low!” Okay, that came out rude, but Senku didn’t believe it.
All those hot things they did. All that lewd hot expression he had. So far, only Senku had seen it. Only him. The thought makes his face hotter. His expression is probably similar to the Mentalist right now. And there’s the pride resurface again. What happened to him? It should be done by now.
“Oh shut up, Senku-chan! What do you think I did when I achieved that popularity at 19! I was working hard, and didn’t have time for this thing!” Oh, that flustered face really suits him.
“Well I guess that's fair.” Senku contains his shock and keeps it calm.
“And what happened to the innocent science boy I know?! I don’t know you’re a player!”
“Ha? I’m not a player! This is my first time too!”
“First Time?! No way I’m gonna believe that!”
Senku exhausted, he just want to relax, so he come back to dip his body in the warm water. And closing his eyes, relaxing against the rock. “Believe whatever you want, Mentalist. And thank you for the compliment.” Senku let out a snicker.
Senku could feel the water ripple beside him. “Alright, if it’s your first, then how?”
“How what?” Senku opened his eyes and let out a smirk toward Gen. Gen is red again. Senku will tease him more in the future if he would have this reaction. He acts like a highschool girl.
“How is it so good?” Gen pout at that, probably knowing Senku’s teasing him.
“Well I did research before. Y’know, biology and all. So, I know that people are typically sensitive in certain areas. I’ve read some people's description about their sex play, for possible future needs. Generally I read sex with women though. Didn’t know that the first time I used the knowledge was to a man.” Gen body’s become tense.
“After knowing it, and practically using it, my conclusion was that whether female or male, the play would still be the same. The difference would be on the organ, that leads to different preparation, and the implication.” Gen somehow looks like listening closely.
“A.k.a, not much different in the execution part.” ended Senku and resumed closing his eyes and relaxing. “Though technically I can't say that, because I don't have other variables to make a comparative study.”
“But that’s theory, not practical knowledge.”
“Then you can say I’m lucky, in today’s trial and error.” Senku remembering this night how easy it was to find Gen’s prostrate, or his sensitive part, or his preferably foreplay. Or how their kinks complemented each other? The bite thing definitely comes from Senku’s but turns up Gen’s liking it too.
He wouldn’t discover it if Gen wasn't out of nowhere wanting to be fucked, though. Realisation hit him, literally opening his eyes.
“Wait, you never did this, and yet, you're the one making the moves first.” Gen who’s in the middle of washing his hair jolted in surprise with a sudden comment. “I don’t think for a man who has never had sex before, in the middle of desperation, the first thing to do is to be a bottom. Usually they start with something familiar, which is to be a top.”
“Ugh stop it! I don’t know, okay! It’s the aphrodisiac talking!” as if he doesn’t want to hear anything again, he rinses his hair.
“Well you still can describe what happened or what you feel.”
Gen let out a shy pout. “It’s like my inside involuntary pulsing, like it needs something inside. I try to ease that by stimulating my cock, but it’s no use. Then I try to use my finger, it subside but it’s not enough. Even after I- I came, the feeling was still there.” Gen takes a glance toward Senku. His face flushed.
“So that’s why I need your help. When you purposely thrust that part while pressing here.” Gen looks at his stomach and pressing the area where his prostate should be. “Instant relief. Like, finally I’m not in agony anymore.”
“The aphrodisiac probably increases sensitivity. Probably your dose increases the prostate sensitivity to the point that it has to be stimulated. If you said it earlier I can help you sooner.” So he had to have penetration from the start. That must be frustrating.
“Well you’ve helped me, Senku-chan.”
When they came back to the observatory, the reality of what happened a couple hours ago hit them. They stood there watching the mess they’ve made. The jars were toppled, spilling the water and oil all over the floor. There are a couple of scratches on the wood floor. The air is humid with the smell so prominent that he can only give the label the smell of sex.
And don’t get started with the futons. They are torn. There is cum on it. Blood stain, probably from his back and Gen’s chest. And another stain. Is that urine stain?
Senku takes a glance toward Gen beside him. Both of his hands covered his face. But Senku could see the redness on his ears.
“You really are a baby.”
“Waaa, shut up, shut up, shut up!.”
“It’s perfectly normal, Mentalist. Prostate was located near bladder, so when the prostate was stimulated repeatedly–”
“Alright alright! Don’t say it out loud, Senku-chan!” Gen almost instantly goes to the futon. “Now help me burn this.”
They burn it. It almost looks like a campfire.
Then they clean the observatory so it looks like it never changes. When they searched for a clean futon, they only found that there was only one spare futon.
“I’m familiar with this kind of luck. You used all your luck for the sex, Senku-chan.”
“Just sleep together, you wouldn’t remember because of the tiredness anyway.” Senku already lay in the futon and turned his body, so he could face the wall.
Senku can feel the ruffle of the futon as Gen laying down. Senku couldn’t feel Gen’s heat. It’s weird. So Senku took a glance and found out Gen is not entirely in the futon. Senku decides to pull Gen by the waist so he is fully in the futon.
“Wh- what Senku-chan?”
“Shh, sleep.” Senku feels the heat pretty comfortably. So he kept essentially hugging him from the back.
Before Senku’s consciousness drifted, he felt a couple of regrets in him.
Once, he didn’t take a look at Gen’s messy release that makes ‘that’ stain, with his own eyes. It's highly possible it happens when he’s on his stomach. Now he rewinds his memories, Gen did want Senku to stop. Yeah, even if he knows it, he, 10 billion percent, won't stop it.
Second, till the end, he didn’t get the chance to taste those lips. What a bummer.