Chapter Text
It starts with one.
It always starts with one. Just one kiss, one cigarette, one beer then I'll go home no for real this time I swear - or, in Tsukasa's case, just one kid with big teary eyes clutching the hem of his lion pelt while pulling at his heartstrings, producing fairly annoying sounds like a broken violin.
This has been going on for a solid hour. A whole three thousand six hundreds seconds - as Senku kindly reminded him earlier - of Tsukasa seemingly being trapped in stone again, not daring to move around lest the child might let go of his cloak and then they'd have a tiny human with zero survival instinct lost in the woods.
Which would be tiring. Probably slightly stressful, too.
And so Tsukasa stands frozen in the middle of the crowd, eyes occasionally darting to the one meter high disaster clinging to his side, waiting for any kind of relatives to show up and claim the tiny bundle of nerves.
It does not happen.
Senku's right foot taps on the ground in a rhythm and joins the cacophony, meanwhile Tsukasa pointedly looks elsewhere.
His gaze glides over the mountains, over the lines of freshly depetrified people being guided to their new accomodations after too many tearful reunions.
It lingers there, on the intertwined fingers of lovers and family meeting again after thousands of years trapped in stone, on the tears stuck in the crinkles of a grandmother hugging her grandson again -
- then on the tiny fist balled around the fur pooling from his shoulders and the painful absence of another adult to hold it.
He knows what it feels like.
He knows how much space absence can actually take.
The meadow slowly clears of the new waves of revived people. They've been working fast, bringing back hundreds of them everyday in different places across the country now, providing shelter and tediously registering all of the revived person's names and whereabouts inside their freshly running informatics system.
It is a grueling task, one which would probably take months to complete. However, the more people they revive, the more workforce they get to do just that.
Senku could have easily sat that one out in favour of staying in the lab and letting others handle it, yet, Tsukasa suspected that the grumpy scientist actually enjoyed it - to see the gaze of utter bewilderment and awe whenever he poured the revival fluid he created on the statues, feeling like what he did truly mattered.
Smiling as his goal of reviving all of humanity slowly, steadily comes true under his watchful eyes.
He fought tooth and nails to get there, and now they are.
The scientist, thriving in his new labcoat and always frantically scribbling things in his notebook with a grin, is truly a sight to behold.
Yet, Tsukasa's attention still won't drift back to Senku and his ruffled aura just now.
Not when he's glaring daggers at him as he flips his notebook shut with a passive agressive clap.
The scientist clears his throat, and the brunette stares at a flock of cranes crossing the slowly darkening sky, until Senku decides that he won't let his comrade - partner, lover, his everything really - ignore him for one more second.
The latter already knows where this is going. Families and friends have all reunited by now, but the child is still annoyingly there.
And Tsukasa's hand is dangerously close to holding the kid's tiny fingers too.
Yuck.
"No. Ten billion percent no." The blonde snips as his wary eyes dart from Tsukasa's head lost in the clouds to the little chestnut mop of hair peaking from under his heavy cloak.
Why on earth did the frightened child decide to hide there, Senku couldn't tell. Maybe the lion pelt reminded her of a plushie she may have had in the old world, or maybe Tsukasa's protective stance and warm half-smile are just that compelling, who knows.
Who cares.
It's not supposed to be there.
The latter's neck snaps back into place, torn away from the cloud of chirping black dots flying between them and a setting sun dipped in gold. Senku seeks out his gaze, lips pursed and both hands on his hips, obviously standing strongly on whatever decision he has already made.
"I haven't even said anything yet." Tsukasa recoils with an indignant huff, and Senku's left eyebrow twitches.
"You don't need to. I know that face. It's your savior-complex clocking in and sucker punching me in the guts. You know I'm weak ! Have some pity and drop the kid on someone getting more than four hours of sleep a night and with some patience for something else than crappy experiments." He berates, and Tsukasa shrugs his shoulders, sending the pelt to billow around him and covering a bit more of the kid.
"That child is by no mean responsible for your shitty sleeping schedule and irresponsible lifestyle. You just met her."
"But she will be !" Senku barks, two millimeters away from disintegrating or sending the notebook straight into Tsukasa's face. Both options are plausible. "I'm already running on fumes here. I warn you, if you add any more chaos to my plate, I will start drinking Ryusui's disgusting whisky and then you'll have a kid AND an alcoholic boyfriend."
Tsukasa only shrugs. Senku is already such a handful - he probably would cause less of a ruckus if stuck in bed to sober up.
"I will easily carry you and put you to bed when you'll pass out. It is not a problem."
He smiles, and Senku's brain stutters.
"What ? Dude, no. For real, Tsukasa, put that back where you found it."
Both their gazes circle around the now empty meadow, all Senku's hopes of help swept from under his feet.
Everyone else is gone by now.
"At the bottom of the swamp we've been pulling statues out of for the whole afternoon? Rude, Senku, even on your standards."
The fondness in Tsukasa's eyes shows he doesn't believe he would do it.
"Of course not ! Just... give her to someone else." Senku waves his hand dismissively, as if he were trying to shoo away some kind of fly or worst - some kind of feeling like pity. "Someone who won't blow her up along our hut next time I play with chemicals that should never be found out of a highly reinforced and guarded military facility."
Tsukasa snorts, then motions for the fist still desperately coiled around the hem of his cloak.
"But it's my pelt she's holding." He protests with a drawl, and okay, fair - Tsukasa is using psychological warfare by now, fluttering his dumb long lashes and twisting his lips in a barely perceptible pout, just enough for Senku to want to pull him down by the hair and bite them.
Fuck.
"Tsukasa." The scientist seethes. "You're the goddamned strongest man alive in this world, and you're trying to make me believe that you cannot unlacth a kid from your hip with just an itty-bitty little nudge of your finger ?" He accuses, and Tsukasa blinks back.
"I never said I couldn't. Only that I didn't want to." He elaborates, his voice even and unbothered despite him basically declaring that he would take care of one unknown frightened child just because said child apparently decided this was how things would go.
As if their hut could accommodate someone else.
Despite the modern civilization up and growing day by day, they were still there, piloting operations from what used to be Roppongi Hills and then Tsukasa's lair, and where they now have slightly sturdier wooden houses and electricity. Still...
This was a bad idea through and through.
Not that they haven't been around kids before, but Suika has been used to take care of herself early on, and Mirai has always been nurtured and protected by Tsukasa.
This ? This is a clueless moderner thrown into a brand new world without any familiar face to welcome her.
And yet...
A quick glance at their surroundings indicates that there is no one waiting for her here.
At least not with today's batch of revivees. Hopefully they'll be lucky tomorrow - the statues of the kid's parents couldn't be that far away, could they ?
Senku drags a hand down his tired face.
"Fine. Let's go back to the village and see if someone, who is not us, can take care of that child for tonight."
So of course this ends with the three of them crammed inside their house, since the little girl had the audacity to take a nap while being carried on Tsukasa's back.
Someone, send help.
By the time they make it through the door, she’s awake again, somehow groggy and clingy. As soon as her tiny feet touch the ground, she immediately reattaches herself to Tsukasa’s pelt, as if she never left it.
Senku huffs, tilting his head back like he’s trying to summon patience from the moon itself. "Okay. First step-"
The child sneezes.
Hard. And into the fur.
Tsukasa looks down, eyebrows folding in slow motion. Senku pinches the bridge of his nose.
"...Great. The pelt’s a biohazard now."
They don’t have much to work with in their current living arrangement. Their hut is basically one medium-sized room that includes a small kitchen, one bathroom, and one storage unit cluttered with makeshift shelves, half-dismantled prototypes and many items definitely not safe for a child . It’s cozy if you’re a couple. It’s a disaster if you add a third small human with unpredictable mucus output.
Tsukasa crouches and tries to coax the kid out of his cloak. “Hey there. What’s your name?”
No answer. Just wide eyes and a sniffle.
“Okay, Sniffles it is,” Senku mutters from behind him. “We need bedding. Food. Warm water. Maybe a crash course on keeping children alive.”
“You're very helpful.”
“I’m not a babysitter, just a scientist who sometimes makes soup.”
Senku throws his hands up and goes off to shuffle through their supplies. Said supplies consist of dried mushrooms and aromatics, what’s left of bag of potatoes, a couple of rags and leftover pelts when those were their predominant source of clothing and bedding. It’s not like they spent much time inside of that hut anyway.
Eventually, Tsukasa convinces the girl to let go of his cloak and accept a less sneezeable alternative: one of Senku’s lab coats, which is about four sizes too big. She waddles in it like a lost duck, but at least it’s clean. Ish.
Dinner is an improvisation. Senku boils some roots with potatoes and tosses in a few dried mushrooms with a look that says this will not pass FDA standards. Tsukasa adds some herb garnish because taste still matters, even in crisis.
The kid pokes at the bowl, eyes flicking nervously between them.
“Not poison,” Senku says, deadpan.
“Just eat what you can,” Tsukasa reassures quickly. “It’s really not that bad.”
After a few hesitant bites, the child starts eating properly. Tsukasa watches as if to make sure nothing goes wrong. Senku watches Tsukasa.
“You’re already too emotionally invested.”
“I’m allowed to care.”
“That’s the problem. I don’t want you suddenly sad when the kiddo leaves tomorrow.”
Tsukasa smiles softly. “Don’t worry about it.”
Read: Worry many bits.
Later that night, after too many awkward attempts to make a bed from old blankets and pelts, the three of them end up crammed together. The child lays curled up between them like it’s the most normal thing in the world.
Senku lies rigidly on his back, clearly recalculating every life choice that led to this.
The night is...long.
He spends the first hour lying perfectly still, blinking into the dark while one small foot repeatedly jabs him in the ribs. “I did not fly to space for this,” he whispers to no one in particular.
Tsukasa hums sleepily beside him, only half awake. “You’ll adjust.”
“I don’t want to adjust. I want a bed. And boundaries.”
A soft snore interrupts them. The kid has flopped over, mouth slightly open, one hand latched around a fistful of Tsukasa’s hair. His other arm is sprawled across Senku’s chest like she’s claiming them both through sheer surface area.
Morning comes too fast and too bright.
Senku wakes up with a stiff neck and, well, definitely not more rest than what he's used to. The child is already up, wide-eyed and curious, pointing at coils on the floor like they’re Legos. Tsukasa, hair half-tied and looking unfairly rested, traitor that he is, is cheerfully teaching her how to hold a ladle.
He must have informed their captain that help is needed because Ryusui shows up early, hair glinting in the sun, wearing that grin that says he's about to cause a problem. François follows close behind, buttoned, polished, and immaculate, despite presumably doing the actual work of catering and supporting hundreds of people.
Ryusui leans against the hut's doorframe. “So. You have a kid now.”
Senku gives him a deadly look. “Not on purpose.”
François peers inside, takes one look at the child standing on a chair stirring something in a pot, and turns to Tsukasa with that serene, terrifying calm they always wield when a situation is spiraling. “May I assume this is a temporary arrangement?”
“Ten billion percent. This ends today.” Senku declares while frowning at his disorganized tools.
Tsukasa hesitates. “We’d like to ask for help. She’d be safer under your care. You’re better equipped.”
They both turn to François, expectant.
François bows slightly. “Of course. We can provide meals, and I will arrange for safer furnishings. However, I must politely decline the full-time care of the child. I am currently supervising nutritional plans, sanitation infrastructure, and incident response for over four hundred revived civilians. Placing a child in that setting would risk her wellbeing.”
Senku raises both brows. “So that’s a no.”
François inclines their head. “A graceful one.”
Tsukasa bows in return, sincere, clearly not as indignified as he should be. “Thank you.”
By the time the sun is at its highest, their hut is partially transformed. François has a few people deliver cushions, bedding, actual bowls, and child-sized utensils. The kid lights up at the sight of a sparkly inflated ball, probably Ryusui’s idea. It's not heavy enough to topple shelves and shatter glassware on impact, but still a risk for any unsecured test tubes. The girl waddles around wearing her new sunflower hat and Senku visibly loses a bit of his scowl at the sight.
Damn it, François probably heard the stories of his early accomplishments in the Ishigami village and decided to play the weaponize sentimentality card.
Additionally, they now have a stock of pre-made or easy to reheat food that make it look like they're going on a week-long field trip with a class of middle schoolers. Not that this whole ordeal would last this long, obviously.
This being said, neither Senku nor Tsukasa complains about their generous new stock of rice balls, steamed buns, dried meat, rice crackers and various soup bases. Unseasoned potatoes for many dinners have been…yeah.
Somehow, they manage to convince Ryusui to keep an eye on Sniffles while they head out to handle the latest wave of depetrified survivors to be. It's always the same process: revival fluid, tightly condensed emotional support, registration, family reunification, post-awakening guidance, rinse and repeat.
Things are as typically chaotic as the routine goes.
There’s no pause in the revival effort, and they can’t exactly skip their shifts just because they’ve accidentally adopted a child.
And suddenly
Tickle-tack-toe, here's another child to go!
A mother has misidentified the kid she thought was her son. Understandable, really. Moss, cracks, and thousands of years in stone will do that. No biggie, she got it right the second time, it happens. The issue now is, what happens with the extra kid?
Tsukasa is already crouching beside the boy while Senku is stuck with a sheep stare. He’s no prophet, but he knows exactly what’s about to happen.
“No,” Senku says flatly, with a dryness and tiredness that could have made Tsukasa stagger if he had the energy to throw in some puppy eyes too.
Tsukasa doesn’t look up, still focused on the boy’s confused little face. “We can’t leave him alone.”
Senku rubs both hands over his face. “You said one. One child.”
“I said we wouldn’t leave one,” Tsukasa corrects gently.
The boy blinks up at them, still dazed from being abruptly orphaned, un-orphaned, and then re-orphaned in the span of a couple of minutes. Tsukasa gently offers him a hand, which the boy takes, small fingers curling around large, calloused ones.
“What’s your name?”
“…Gaku,” he murmurs, hesitating a little.
“Alright, Gaku. Let’s get you settled.”
The walk back is mostly quiet, save for Senku muttering under his breath about all the variables he should have seen coming and prepared for to avoid this very situation.
They return to the hut to find Ryusui gesticulating enthusiastically, mid-monologue, while Sniffles claps and giggles at something involving friendly pirates and buried treasure. Her sunflower hat is tipped like a sailor's cap, and her face is flushed with joy.
So much for a stern talk about putting an end to all this.
“She’s got a name now!” Ryusui announces grandly as they approach. “Isha! Sounds a bit familiar to me, if you ask!”
“She told you that?” Senku asks, suspicious.
“HA HA! She even corrected my spelling!”
Senku stares at what sounds like a miniature version of his own name, apparently bursting with energy and an absolute danger to the inside of their hut.
Thank fuck Ryusui saw it coming and entertained her outside.
As soon as the flowery ball of energy notices the new kid, still half-hiding behind Tsukasa’s leg, her cheerful clapping comes to a sudden stop. Her eyes widen. She gasps with the kind of awe Tsukasa last saw when Senku discovered a (very much radioactive) monazite deposit during a caving expedition.
“A boy!” she announces, pointing like she’s just spotted treasure.
The boy, for his part, blinks up at her like she’s a particularly loud fox.
“He’s shy,” she adds, delighted, in a way that is not at all self-aware. Then, with unshakable confidence, she marches up to him and declares, “You’re playing pirates with us now! You can be the lookout.”
Before either adult can react, she grabs Ryusui’s hand and drags him toward the new kid, who is immediately welcomed with an exuberant, “Welcome aboard, tiny crewmate!” Within a minute, a flamboyant hat made of folded leaves lands on his head.
The boy hesitates, but when Isha hands him a stick and declares it his spyglass, something clicks. Next thing they know, he’s pretending to spot an enemy ship in the bushes while Isha bravely duels a tree.
Ryusui, never one to stay behind, enters the scene as a sea monster. He challenges both kids to heroic tickle battles, resulting in shrieks of laughter. He hoists the new boy onto his shoulders for a dramatic kidnapping, while their pirate queen chases after him, valiantly attempting to whack his kneecaps with her sword-stick.
Tsukasa watches, the corners of his mouth twitching into a full, warm smile.
Senku, arms crossed and brow deeply furrowed, stares at the unfolding scene like it’s personally violating his scientific principles.
“They’ve known each other for 12 seconds.”
“Children tend to bond quickly,” Tsukasa says, folding his arms, smug and satisfied. “It’s a good sign.”
Senku doesn’t look convinced. “It’s a sign of impending disaster.”
“Or joy.”
“Disastrous joy.”
Tsukasa tilts his head. “Have you seen your face when you’re swirling potentially corrosive, definitely deadly liquids in a flask? You make it slosh in front of your face like you trust that piece of glass more than you trust me.”
Senku’s expression twists. “Excuuuse me?! You did not just compare me to that,” he says, gesturing with both arms toward the gremlin energy explosion happening in front of them.
“I’m just saying, you trust a fragile piece of glass more than you trust me most days.” he mumbles, expertly changing the subject and wearing a fake pout that would definitely make Gen proud.
“I know exactly what I’m doing! Meanwhile, you’re out here letting emotional bombs move into our house.”
Senku pinches the bridge of his nose, which may as well be his new resting state.
“I’m about to rank you below an Erlenmeyer on my favorite things in the world list if you keep going.”
“You have a favorite things in the world list?” Tsukasa asks, smiling, eyes crinkling with quiet amusement.
“I have an everything list.”
“Well, you’re my everythi-”
Smack.
Senku whacks Tsukasa in the back of the head with his notebook and stomps off toward the hut without a word and a hint of a blush.
He’s really not in the mood for sweet talk, not when they can’t even follow through on any of it in their current ridiculous living situation. He’s already pushing his tolerance to its limit and really doesn’t need any more frustration he can’t fix.
Meanwhile, believe it or not, after a day of babysitting and an extra hour of intense pirating in the New World sense, even Ryusui is running out of energy. François, naturally three steps ahead, reappears with a gourmet meal for five, having apparently planned for the highly probable event of an extra child materializing by dinnertime. The extra kid in question now sticks to Isha like glue. Isha, in turn, is firmly attached to Tsukasa, much to Senku’s visible distress.
They glance at their hut. Then the floor space. Then the number of small humans currently occupying said floor space. Then back to their single bedroom.
Senku is already rubbing his temples between two bites. “There is no way this is gonna work.”
Tsukasa surveys the mess of bedding, half-eaten snacks, pirate hats, and at least one stick-sword abandoned mid-battle and sighs. “Storage room.”
Senku stares at him like he just confessed to being anti-vax. “That’s my lab. My workshop. My supply sanctuary.
“It’s either that, or you sleep with a kid in each arm.”
A beat.
“…François.”
The transformation is fast and eerily efficient. By the time the sun starts dipping below the horizon, the storage room is unrecognizably functional. Two tiny futons, soft woven mats, low shelves secured tightly to the walls, and even a moon and colourful stars dangling from the ceiling.
Tsukasa stands in the doorway, a quiet sort of awe settling into his expression. “François, this is…”
“Excessive,” Senku cuts in, though his eyes are fixed on the absurdly whimsical hat rack and a sink stool carved with what appears to be a dragon in a captain cap.
Already, Isha and Gaku have claimed their spots, limbs flopped across the futons as they ramble about treasure maps and jellyfish invasions, voices bouncing off the walls with a kind of energy that should’ve been illegal at dusk.
Senku’s sanity is hanging by a single thread that is the hope of one (1) uninterrupted night where he can cuddle his ridiculously attractive boyfriend in peace, without tiny limbs kicking him in the ribs. A night where Tsukasa is his personal heater and not also serving as the emotional support mattress for two aggressively affectionate children.
Little did he know that Newton’s forgotten fourth law clearly states: Senku is not allowed nice things nor any kind of luck. He’d barely had time to bury his face in Tsukasa’s hair cascading his chest, breathe in that soothing forest-and-sun scent, and maybe, just maybe, start enjoying their well-earned nap, when the turbulent duo came sneaking back in like overly affectionate raccoons.
They squirmed their way into the futon with the stealth of kittens on a mission, wedging themselves between limbs and blankets until “group cuddle” became less of a suggestion and more of a siege.
And just when Senku thought Tsukasa might finally share in his frustration, Gaku looked up with wide eyes and declared, very solemnly, that he was scared to sleep alone on his first night.
That was it. Game over. Tsukasa melted faster than butter on hot pancakes they did not have, and the so-called nap date was officially over. Ruined, in Senku’s words, by his boyfriend’s criminal levels of misplaced empathy.