Chapter Text
In December, the Kingdom of Science is plotting.
Collectively, they’re constructing a phone. They’re plotting to win a war with the second man intentionally revived, Tsukasa. It’s cold, but they have a good few months to focus on improving food technology and to complete two mobile phones. Senku’s head is full of engineering, of strategies, and of various ideas on how to decisively win, how to convince Tsukasa’s people to turn traitor, and, after that, how to convince the beast of an Alpha himself.
Privately, however, Senku is plotting something, well. Else.
Ever since Gen showed up at the ramen stand, asking so delicately for a Cola, Senku has needed that boy to be his partner. Not just in crimes and sins and whatever, but his partner in life. Their minds just clicked. Gen was, as Byakuya sometimes put it, the Jelly to his Peanut Butter. The other half of him. Senku needed to ensure he would come back to his side eternally, and when they died, they would have to be buried side by side.
So.
He was going to get that man pregnant.
So far the plan stood thusly: Get closer to Gen, get him accustomed to some form of intimacy, and then figure out a way to get him pregnant. Operating under the assumption that Gen was an alpha or maybe a beta, given his personality and his popularity in the ancient-modern world, this would be a bit of an odyssey. Alpha males don’t get pregnant, they lack all requisite equipment, but if Senku gets Gen comfortable enough he might consent to some medical experimentation with omega hormones or even gene therapy, if anything like that becomes possible in their lifetimes.
Baby trapping him was the only permanent solution.
This had nothing to do with watching Gen perform magic tricks for the Ishigami Village children, nothing to do with how gentle he was with Suika, nothing to do with how beautiful his face was.
It was purely logical on Senku’s part! Really.
Senku was perfectly aware of his own possessiveness. He was an Alpha with enough confidence to rebuild the world, after all, and he’d always written his name on every single thing. He wouldn’t be able to settle for anything less than all of Gen. Anything less than a legal marriage and rings and children with their combined genetics just wouldn’t satisfy him.
Plus, getting him pregnant as more or less the first step in their relationship would sidestep any reason for Gen to flee. As flighty and eager to save face as Gen was, he wouldn’t be able to handle a blunt confession without getting so embarrassed he just left, and Senku couldn’t have him run into the arms of someone else. He considered the morality of consent for a few moments one night in the Lab, but honestly, as long as Gen consented to the sex, he didn’t care if it was immoral that he intended to impregnate him.
By the time he was gone on his mining expedition, he had a roadmap worked out, written in code on a wooden board in the back of the materials shed.
He comes back to an observatory and Gen confessing to being his fan.
If it weren’t for the war they were fighting, Senku would be tempted to move up his timeline a few years. But no, right now, they had to focus on their main plots, and Gen’s focus needed to be on his impression of Lillian.
And of course they win the war. Tsukasa wasn’t actually trying to remake the world in his image, he was trying to protect something unnecessarily, and was angry at the past for making that impossible before.
It’s killing Tsukasa that takes a toll on Senku, and Gen, naturally, sees right through him.
Gen pulls him aside the night after, and pulls him into a hug, scenting him and talking about the flowers that sprung up, the baby birds he’d seen, the bugs that would be coming soon. It doesn’t take Senku long to fall asleep in his arms, and when he wakes up the next morning, Gen is still there, snoring, with Gen’s robe over them both as their blanket. In the gentle light of morning, Senku promises himself. He was going to get Gen pregnant, before it was too late.
They launch into preparations for making the ship, but now that the immediate danger has passed, they can relax. They can’t slow down production, of course, so they revive Ryusui and Senku has to say goodbye to Gen for several weeks. It’s the first time they’ve been apart for any real length of time since the phone expedition, but at least Gen is safe with Taiju and Yuzuriha and Senku doesn’t mind being distracted by Ryusui.
He’s a tall, handsome Alpha, with the kind of confidence one only gets from having more money than god and never failing to go for what you want.
Speaking of which, as soon as Gen gets back to the village with Francois, Senku has to field a few questions.
“Why didn’t you tell me about your celebrity mentalist? I didn’t know you had such a handsome omega on our side!” Ryusui laughed, watching the (apparently) omega head up to the observatory to lay down.
“...Huh?” Senku tilted his head.
“I knew I smelled an omega’s scent on you, I just couldn’t identify whom! I thought it might be your mate, but you don’t have one, do you? It’s just that Gen’s got his scent over you good, it’s stuck so long.” Ryusui rambled, then went off on a tangent about the scents on some of his friends.
Senku dug up his roadmap and tucked it into the glass furnace.
Over the course of that winter, things are forced to slow down. You can’t work in the snow, so various ploys are made to make more drago and encourage leisure activities and ensure warmth and health. It’s before valentine’s day that Senku is able to broach the subject with Gen, up in the observatory, watching the Ishigami kids build a snowman under Ukyo’s guidance.
“You’re an omega.” It’s a fact, so he states it as one.
Gen is pouring some tea and nods, like it was obvious.
“...but you don’t have to find a safe spot for your heats like the others. The village has a hut, you know. Yuzuriha built a safe section of the caves that Taiju and Tsukasa guaranteed protection of. You don’t sneak off for three to seven days a month, I’d notice.”
“Well,” Gen gathered his thoughts, handing Senku his cup, “I’ve got a condition, you see. Silly thing really. It was convenient, actually, when my schedule was so tight back in the modern era. My scent is very slight, and my heats are incredibly weak. I didn’t need to do anything special to work around them for my shows.”
“Sounds pretty convenient.” Senku sipped his tea, waving at Suika when she noticed them.
“It is! There is, of course, the atch-cay.”
Senku glanced back at him, imploring him to go on.
“Even in the modern era, it was unlikely that I would be able to have children. Not the pregnancy itself, I'm not at a much increased risk of miscarriage, just the functionality of getting pregnant itself would be difficult. It’s entirely possible that I’m completely sterile, since my eggs don't drop right.” He shrugged.
So, there was a different wrench thrown in Senku’s plans, but this was one he could work with.
By Summer, they were sharing casual skinship like it was nothing. Senku could stand still and have Gen come up next to him, within an arm’s reach or even leaning on him. They helped each other into the motor boat. Gen slept in a bedroll next to him, they bathed in the same area of the river. The tiny swim shorts Yuzuriha had made Gen were nothing short of a distraction.
It was hard to imagine Gen anywhere but at his side once again, and Ryusui made sure to bring him on the boat when it was ready.
Their first stop had its own major complications, but Ryusui sent Gen with Senku on the survey team for two reasons and they both knew it. The first was his social skills, naturally, but the second was so Senku wouldn’t be without his… well, Ryusui hadn’t flirted with Gen at all. He knew when he needed to leave things alone.
When it became necessary to dress someone up to sneak them into the harem, Senku panicked. Of course Gen could pull it off. He was an omega, just add a few extra curves and raise the voice and he practically was a woman. The slit in his dress signalled so much, right up the middle, like he was inviting someone between his legs, and Senku had to stop him from going to the selection.
Not only to keep Gen at his side for strategic thinking, but also to protect his omega from being touched by anyone else.