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1 - Before the War
Gen was smiling, which Senku had quickly learned was either a very good sign or a very bad sign.
When the fraud magician had first shown up, Senku considered him as little more than an extra set of hands for labor. Tolerable at best, able to charm his way into the village and keep the children occupied - a decent enough ally in a world turned to stone. But over time, his esteem for the mentalist had grown.
Gen wasn’t the shallow man he purported to be, not really. Yes, he could be lazy and a bit of a whiner, he could be absolutely obnoxious and always seemed to know the right nerve to press if he really wanted to piss him off, but those negative traits only served to highlight his more redeeming features.
He was observant and resourceful, his knowledge of personalities and situational awareness not only useful for stopping conflicts, but at identifying solutions Senku never would have thought of.
“Always pick a lazy person to do a hard job, they’ll find an easy way to do it.”
Byakuya had always made that joke when finding little shortcuts, and Senku found himself replaying the words in his head more and more as he worked with Gen. Gen’s form of laziness led to creative thinking, often improving processes or finding someone better suited to a task despite initial plans - and while in many ways he appeared self-serving, one only had to peel a layer or two back to see the true intentions behind his strange behaviors or how they ended up benefiting those around him.
Yet still he hid behind the mask of the most shallow man alive. A paper thin shield, easily seen through by anyone willing to look just a little closer, and one Senku still struggled to truly understand. While annoying, he knew well enough to let it be for the time being.
Gen was cunning, he wasn’t above trickery to get what he wanted, but at the end of the day he wasn’t cruel or malicious.
So when Gen climbed up to the observatory and started to explain his scheme, his clever plan to use the glass record and his impersonation skills to deceive the members of Tsukasa’s empire and get them a leg up on the upcoming battle, Senku wasn’t surprised.
What he was surprised by was the thought forming in his head with the clarity of a perfectly solved formula.
I’m gonna marry this guy someday.
It hit so cleanly, so matter-of-factly, that it didn’t even occur to him to be startled by it until several seconds later, and by that time Chrome had made his presence known and shifted the conversation. He forced the errant thought back into whatever mental drawer it had burst out of, focusing instead on fleshing out their plan.
“The rest will work itself out,” Gen cackled at Chrome’s disbelief, a devious expression on his face that Senku found himself mirroring.
“Exactly the sort of low-down, underhanded plan I’d expect from a con artist like you,” Senku agreed, cackling along and feeling that same startling certainty stir again, quiet but unshakable.
Definitely gonna marry this guy someday.
2 - On Treasure Island
When Gen unpetrified for the second time, Senku’s heart did a thing. A dangerous thing. A permanent thing.
For a split second - just a blink - there was no Kingdom of Science or Treasure Island, no plans or projects or world to rebuild.
Just Gen, collapsing forward as stone fragments and dust fell from his shoulders. His eyes blinked open, squinting against the afternoon sun, color returning to his cheeks and arm slowly lowering from its raised position.
“Remind me never to do that oluntarily-vay ever again, Senku-chan,”
Senku’s hand lifted to steady Gen as he began to fully register gravity again, shifting to accommodate as the other man leaned into him. There were no dramatics or theatrical flourishes, just a relieved, instinctive press of weight - expecting Senku to hold him up.
Trusting him to.
“Whatever you say, Mentalist,” he replied, hoping his face wasn’t doing anything too embarrassing. He could see the way Gen’s eyes roamed around, taking a mental headcount of every familiar face before he managed to find his feet under him, and shook his head slightly.
Gen spent most of his time looking after everyone else in their little group. Anticipating their needs, planning for the future, always on the look out for any little piece out of place or out of sorts - it was one of the things Senku adored the most about him.
But it also drove him absolutely insane.
Because Gen was viscerally opposed to anyone else looking out for him, which meant that Senku had to be very careful in his approach when he was given the opportunity.
“Surprised you're not complaining about being one of the last revived. Everyone else just keeps talking about how much better they feel after being petrified, fucking weirdos."
Senku could feel Gen relax in his hold, the mentalist letting out a small laugh, “Considering I’m not at the bottom of the ocean, is it safe to assume that we won?”
The idea of Gen’s statue shattered into pieces and sinking to the seabed, left for centuries to erode and decay, sent a stabbing ache through Senku’s chest and unconsciously his hold tightened on the other man. He wasn’t sure how long the silence lasted, jolting back at the gentle touch of Gen’s hand on his face. His palm was warm, eyes concerned, and Senku felt something in his chest give a little flip.
Unsure of what else to do, he started to explain what happened after Gen and the others were petrified because the alternative was blurting something incandescently stupid like You’re not allowed to die because I’m going to marry you one day, you idiot.
3 - En Route to South America
If asked, Senku would have said that getting shot ranked in the top five most painful things that had ever happened to him. What he wouldn’t say was that the uncertainty of Gen’s welfare in Xeno’s base had ranked higher.
“I thought I told you to rest.”
Senku looked up from the desk he was perched at, eyebrow raised sardonically, “You said that if you caught me in the lab you’d break my knee caps.”
Gen rolled his eyes, pointedly setting the tray in his hands on top of the schematics Senku was working on, “You know what I meant. Back in bed. Now.”
“But this isn’t strenuous-“
“Says the man who participated in an aerial dog fight with several bullet holes in his chest,” Gen yanked the chair away from the desk. “Orgive-fay me for not trusting your judgement.”
Sighing, Senku tossed his pencil down and maneuvered onto the bed. “Don’t know why sitting in a bed is different than sitting in a chair,”
“Because I said so,” Gen shoved a cup of tea into his hands before turning to tidy up the project Senku had left behind.
Senku took the moment to observe the other man. Gen’s expression was soft, but there were dark circles under his eyes, creases of exhaustion pulling at his mouth. Between Senku’s own injuries and their sudden need to escape from Stanley, there had been little time to really sit and digest everything that had happened, but now…
Now, the familiar sight of Gen fussing over his work after forcing him to rest seemed to cut through whatever remaining tension Senku still had in his body. He’d known subconsciously that he’d missed having Gen around, but it truly hit at that moment, his own exhaustion making itself known. Bone deep but with a softer, warmer slant - the kind of tired that came from cozy winter nights talking over hot drinks, the quiet domesticity of working together with no need for conversation because silences were never awkward.
And with that realization came a second - Gen was his person.
Not because he was useful, or brilliant in all the ways Senku wasn’t, or because he seemed to always come back no matter what.
But because he chose Senku every single time. And Senku chose him in return.
“Stay with me,” he said without thinking.
Gen paused, glancing back at him with a questioning look.
Senku shifted over to make more room on the bed, though there wasn’t much to be made on a twin sized mattress. “You look like you haven’t slept in days. If you stay with me you’ll know right away if I try to get up again.”
Gaze shifting between the open space on the bed and Senku for a long moment, Gen hesitated. They’d slept in close quarters before - the material hut had certainly not been built for three people, especially considering how Chrome sprawled out like a starfish - but they’d never actually shared a bed.
But when Gen finally turned off the light and climbed in next to him, when they awkwardly shifted around until settling down with Senku flat on his back and Gen pressed against his side, Senku wondered why they never had before.
The warmth of Gen’s body and the soft rhythm of his breathing easily lulled Senku’s already exhausted body towards sleep. And as his fingers idly brushed over Gen’s back and shoulder, as the weight of Gen’s head on his chest grew heavier, a thought occurred
I want you to be the first thing I see every morning when I wake up.
4 - The Second Mass Petrification
While Senku understood the logical reasoning for the order of revival, it still pained him to leave Gen a statue. He recalled Gen’s obvious discomfort with the notion following Treasure Island, the lingering unease any mention of petrification brought him that even relentless humor couldn’t hide from Senku’s watchful eyes.
How he made a point to fidget and make noise whenever it was too dark to see, if not just to prove to himself that he could still hear and move. Gen was far braver than anyone could imagine, but petrification had left him with more scars than the one on his face.
Senku hesitated in front of the statue, surprisingly clear of debris despite the years that had passed, and silently thanked Suika for taking care of all their friends in his absence. On the surface his expression was serene but Senku could see the unmistakable signs of the terror and dread he’d been feeling in their last moments, feelings Senku could relate to well.
He reached up and brushed a thumb over the rough surface of Gen’s cheek, finding it cold against his skin, “I’ll be right back for you.”
Gen didn’t reply and Senku didn’t step back until he heard Suika call for him, but something in his chest tightened with every step away he took.
Once enough revival fluid was created and the statues had their time-worn and damaged clothing replaced by leaves and branches, Senku wasted no time in dispensing it.
Stone crackled, a breath hitched, and Gen gasped into waking life as if jolting up from a bad dream. He blinked blearily, eyes focusing on Senku and relief washing over his features so quickly it was like a physical force. “Oh good, you’re alive. I was worried I’d have to aunt-hay you.”
Senku, who had crafted several witty and scientific comments for that moment felt his mind go blank with relief, finally managing to croak out, “Yeah, I’m alive. No haunting necessary.”
Gen took a step forward and stumbled, but Senku was right there to catch him.
“You okay?”
He felt Gen’s head rest on his shoulder, arms coming up to circle his back as fingers gripped the fabric of his new coat - an anchor rather than a desperate cling. “I am now.”
The quiet admission shouldn’t have hit as hard as it did, but it made Senku’s chest feel full and too tight at the same time. It was rare for Gen to voice any sort of emotional weakness, any sort of need beyond the physical ones - sleep, food, sweet treats.
He didn’t like to admit when he was scared or upset, always put on a brave face or a mask of indifference - always putting his all into taking care of others without letting anyone else take care of him. But with Senku he never hesitated.
“I’ll make sure you’re never alone again,” Senku said plainly, because the truth should be spoken with clarity. “Not if I can help it.”
Gen’s breath stuttered and he pulled back to look up at him. Swallowing thickly, he let out a soft breath of a laugh, “Careful, Senku-chan, you keep saying stuff like that and I might start to think you’re in love with me or something.”
Senku didn’t even blink. “I am.”
Gen froze. “…you are?”
“Yeah.”
There was a beat of silence and another, and Gen’s eyes widened and his mouth worked uselessly as color raced to his cheeks.
Senku rubbed his palm over Gen’s back, the warmth of his skin another clear sign that he was there - alive, safe - and realized that almost every decision he’d made since Gen wandered up to that ramen stand had quietly bent towards him.
Not fate or destiny or any other cliche that would have Yuzuriha cooing and Ruri brought to tears.
Just choice.
“You’re my person, of course I’m in love with you.”
Gen made a sound that could’ve been a laugh or a sob, hiding his face in Senku’s neck. “You can’t say stuff like that! I’m not even wearing pants right now!”
Senku rolled his eyes, “So? It's not like I love you for your pants, they're a total non issue in this situation.”
The sound Gen made was definitely a laugh that time, and Senku could feel his smile against his shoulder. “I can’t believe you. You tell me you love me and I’m wearing shrubbery.”
“If I waited for you to look presentable I’d never get anything done.”
Gen swatted at him weakly, but his hand lingered on Senku’s arm and he made no move to pull away. Senku listened as he muttered to himself, knowing the smile on his own face had to be stupid looking as hell but not particularly caring.
I want to be the person you let take care of you.
5 - The Moon Mission
As launch day approached, Senku found himself hyper-fixating on cataloging every single possible thing with a precision that went far beyond standard engineering.
Every bolt, every wire, every gauge was inspected with a critical eye, triple checked with each calculation redone from scratch. Every risk considered, every solution fleshed out, all possibilities weighed and balanced again and again.
But between those calculations was Gen, standing on the periphery with a too-wide smile and his hands tucked into his sleeves. Not a distraction, but as a constant value in the equations, a factor all the others circled around. And as the hours crept to early morning, it was Gen still with him in the lab when all the others had retired for the evening.
“Someone’s essed-stray,” he sing-songed as he wandered closer, reaching up to tug on a stray strand of wild hair. “You’re getting all frizzy, very mad scientist chic.”
Senku didn’t look up from the module he was pretending to re-calibrate. “It’s humidity,”
“It’s worry,” Gen corrected and Senku set his screwdriver down.
He hadn’t wanted to have the conversation there, hadn’t planned to, surrounded by the hum of machinery and the sterile smell of the lab. He’d pictured it happening in private. In their living room or their bedroom after dinner or right after waking up - some time soft and gentle.
But when Gen looked at him with that crooked smile of his, the one he only ever used with Senku, the one that said you don’t have to pretend with me, Senku felt something click into place with the inevitability of gravity.
“When I go up there,” he started, voice far too light and casual, “odds are something will go wrong.”
Gen didn’t flinch but his smile dimmed slightly.
“And if something goes wrong… there’s a chance, however statistically rare, that I don’t come back.”
That time Gen’s breath hitched, a small sound but it might as well have been a shout in the quiet room. He reached forward, pulling Senku to face him and leaned close, pressing their foreheads together.
“You’ll come back,” he whispered, arms looping underneath Senku’s to wrap around him, palms curved over his shoulders in less of an embrace and more of an envelopment. “We’re both horrible little cockroaches of men… you always come back.”
Senku could’ve lied to him, given honeyed words and empty platitudes, spouting off scientific theories and probabilities to sooth his worry. But that wasn’t how their relationship worked. It wasn't how they worked.
Neither he or Gen ever shied away from the truth. Gen deserved honesty. He always had.
“So,” Senku continued, circling his own arms around Gen in return, pulling him even closer with a firm press between his shoulder blades, “there’s something I want to tell you before I go.”
Swallowing thickly, Gen’s grip tightened, fingertips digging in and gripping the fabric of his lab coat as though grounding himself- and he nodded for him to continue.
“When I get back,” Senku said, pulling back far enough to look Gen in the eyes, finding his lashes trembling and tears welling but his expression determined, “I’m going to marry you.”
Gen froze so completely it was almost comedic, breath stuttered and eyes wide, like someone had accidentally re-petrified him.
“…you’re going to what?”
“Marry you,” Senku repeated without hesitation. He’d spent the last several years sure of the fact, there was not a single part of him that questioned the decision.
Gen squeaked, face flushing scarlet and a squawk of consonants catching in his throat as he tried to formulate a response. “Senku-chan! You can’t just… this isn’t… you can’t propose before flying off to the moon!”
“I’m not proposing,” Senku raised an eyebrow, pinky digging into his ear idly as Gen boggled at him. “That would mean I was asking. This is just information. I’m telling you the plan so you’ll be ready when I get back.”
“That’s orse-way!” Gen practically shrieked.
“Don’t see why,” Senku shrugged. “It’s pretty obvious. I love you, you love me, I want to spend the rest of my life with you. Honestly, marriage is the most efficie-“
Gen slapped a hand over Senku’s mouth, “You are a menace,” he muttered. “You don’t just tell someone they’re going to arry-may you.”
Pulling Gen’s hand from his face, Senku gave a gentle stroke of his thumb over his knuckles. “I mean, if you don’t want to…”
“Of course I want to!” Gen huffed, looking off to the side as if it would somehow ease the flush of his face. “But you can’t just… drop that on me before you go… gallivanting off to the moon.”
“Why not?”
Gen looked back at him, still red but expression assertive. He cleared his throat and pressed a kiss to Senku’s mouth - a short peck, barely a kiss at all as far as Senku was concerned. “When you come back you can ask me operly-pray. Preferably in an overly dramatic way that will annoy absolutely everyone.”
Senku laughed, able to easily understand the intended message behind his words and what Gen wanted to hear in response. “I’ll come back.”
“I know you will,” Gen grumbled, leaning up to press his lips to the space on Senku’s forehead between his petrification scars. “If anyone can, it’s you.”
Senku felt his breath whoosh out of him, not because the gesture was unexpected - it was one of Gen’s preferred ways to express affection - or Gen’s confidence in him. But because it felt like something he wanted to protect more fiercely than anything else in the world - this feeling, this moment.
This person.
Pulling Gen flush against him, arms wrapped tight and face buried in the other man’s neck, Senku felt his frayed nerves relax for the first time in days.
I want to build the new world with you. Every single step.
+1
In the end Senku’s proposal was dramatic, but not because he planned it that way. Gen knew that Senku wasn’t capable of intentionally causing drama for drama’s sake, he just had a knack for doing things in such a way that drama couldn’t help but follow.
It didn’t help that returning from the moon tended to be a rather high-stakes, attention-grabbing event and the man he was in love with had absolutely no sense of situational awareness or decency.
Because the moment Senku’s feet hit the ground, the crowd surging with cheers and applause and tears, his gaze zeroed in on Gen. Tucked away near the back of the group, hands in his sleeves, smile trembling at the edges and eyes bright - Senku didn’t even bother finishing the conversation he was in before marching straight through the crowd to haul him into a kiss that had the entire Kingdom of Science shrieking in delight.
“Hey, Mentalist, wanna get married?”
Gen laughed as their audience lost it, tears streaming down his cheeks but his smile so bright it put the sun to shame, “Sure, why not?”
The ceremony itself was supposed to be small. Private. Simple. Unfortunately, that plan lasted all of thirty seconds before all of their friends began to chime in.
Ryusui called for a celebration to put all others to shame, Kohaku and Suika were adamant on a veritable mountain of flowers and delicious food, Yuzuriha designed an array of suits and dresses for all those in attendance, and everyone else added their own little touches. And after getting through laughter, explosions, and the chaos expected in anything the Kingdom of Science did, Senku found himself in front of Gen beneath a familiar tree festooned with crude and time-weathered Edison bulbs.
Gen stood uncharacteristically still. No flamboyant gestures or sly smirk, no playful winks or distracting comments, no mask at all.
Just… Gen.
That man who drove him absolutely insane and grounded him all the same. Who challenged him, supported him, comforted him, and refused to let him carry the weight of his goals alone.
The man Senku had been choosing day after day for years.
“Senku-chan,” Gen said softly, voice thick but steady as his fingers gripped Senku’s in the space between them. “I hope you know I’m only doing this because you’re devastatingly handsome, ridiculously brilliant, and very stupidly in love with me.”
The crowd laughed. Senku didn’t.
“Yeah, I am,” he agreed easily. “Because you’re the one person I want with me in this new world. Every discovery, every breakthrough, every stupid mistake and failure. Every day.”
Gen swallowed, looking like he might cry or faint or combust. Or all three.
“You can’t say stuff like that in front of everyone,” he whispered, eyes shimmering.
“Why not?” Senku shrugged, smirking wide. “It’s the truth.”
Gen made a strangled noise like a laugh-sob, pressing their foreheads together. Senku felt his smirk turn into a grin, one so wide he could feel a twinge in his cheeks, deciding that the last few weeks of anxious planning were worth it as he stared into a familiar face-
“JUST KISS ALREADY!” Chrome shouted, half of the village echoing him.
And Senku did, nudging Gen’s head just enough to catch his lips.
And like a spark in a vacuum chamber or the ignition switch to a rocket or an equation that finally balanced…
Everything clicked into place.