Archive of Our Own ^beta

Chapter Text

They’re having dinner one evening, a few weeks after Taiju broke out of the stone, when Taiju pauses in the middle of chewing on his roasted mushrooms on a spit. He makes a thoughtful face and says, ”Senku, I thought of something.”

Senku immediately knows this won’t be good. Taiju has said that exact same thing to him before, and the last time he did, half of a launch platform ended up in the river and then the city authorities showed up.

”If it takes a really long time to figure out how to depetrify people,” Taiju continues, unaware that Senku is having a flashback, ”we could also make new ones between the two of us!” The biggest grin spreads on his face. ”We could literally be Adam and Eve.”

Senku looks at Taiju.

Taiju looks at Senku like he thinks he has just had the Best Idea Ever.

Senku puts his face in his hands, draws a deep breath, counts backwards from ten and composes himself. If this was any other guy, Senku would kick his ass on principle. However, it’s Taiju. This is going to require something more. ”I see. There’s a couple of hitches in that plan, you know.”

Taiju nods eagerly, like he’s waiting for Senku to iron out the details.

”Problem number one: we would only be able to make a very limited amount of new humans.”

”That’s why it’s a back-up plan,” Taiju says reasonably. ”I didn’t mean we would have to do it like right away.”

Senku resists the urge to put his face back in his hands. ”Great. Okay. Problem number two: those new humans would have to be taken care of for years before they could so much as feed themselves.”

”I could gather lots more food so there would be enough for everyone!” Taiju looks at him earnestly. He probably could, too.

”I’m sure, big oaf. Problem number three...” This is not something he likes to talk about much because it might give people ideas, but if he's going to be thorough about this... ”We don’t know if my reproductive system would go online if I took out my implant.”

”Oh, yeah.” Taiju looks worried for a moment, but then he brightens. ”But you said once that the younger someone was when they tried that, the more likely it was that it would work. We’re pretty young!”

”True. But that takes us to problem number four: taking the implant would leave an open wound, which could get infected, and giving birth is achievement for the body. Both of those things are major health risks in a stone world.”

The first signs of doubt start to cloud Taiju’s face. ”Oh, that’s true. We don’t have disinfectant or anything. That’s not good.”

”We would need much more than that, but brandy works as a disinfectant,” Senku tells him, because at some point he has become invested in figuring out the logistics of Taiju’s terrible idea.

”It does?” The big oaf gets excited again. ”But that’s great! We’re making brandy, so we could also use it for that!”

I know, Senku thinks. That’s why I said it, damn me. ”And giving birth?”

”I remember that video about childbirth that they showed us in health class,” Taiju continues. ”It looked real scary, but you’re totally smart enough to figure it out.”

Taiju is so hung up on this. It would be the easiest way to shut this conversation down permanently, but Senku doesn’t have the heart to tell him that with his narrow hip structure, he would probably need a Caesarean section because he couldn't squeeze a baby out through his pelvic outlet. Taiju wouldn’t realise what that meant unless Senku explained it to him, and once Senku did, he would have nightmares. The big oaf even had nightmares after Senku showed him the single stitch he got for his first implant. ”Thanks for the vote of confidence, and I’m glad you’re giving this some thought, but there’s still problem number five.

”Okay! What’s that?” Taiju waits attentively, unaware that Senku is about to pull the nuclear option on him.

”That's the part about starting a pregnancy. How do you think we would handle that?”

Taiju looks at him guilelessly. Senku can almost see the slow crunch of the gears in his head. He waits, but the wires are not connecting.

”Did you think we would get an appointment at the clinic, and a nice nurse would give you a plastic cup and a dirty magazine and leave you alone in a room?”

It takes a few seconds for that to sink in, and then Taiju’s face finally morphs into the blind panic that Senku has been waiting for. ”No—I don’t–that’s–no—Senku–I’m not–!” he shouts, flailing his arms hard enough to fling one of his mushrooms into the undergrowth. He teeters precariously for a moment and falls onto his back with a thump.

”Our options are currently limited as hell.” The next mushroom is toasty enough to crunch in his teeth when Senku bites into it. ”Sperm cells don’t stay viable for very long without some kind of a medium,” he continues, chewing loudly, ”so moving them straight from one body into another would be best. Though I guess we could also use a clean container and suck then into a boiled straw. It just won’t be as sure-fire as the natural method. Do you think you could aim into a pot?” The mushroom below the crunchy one is even more overdone. He should move the rest of them back from the fire.

”Can we please stop talking about this?” Taiju says feebly from the ground. ”I think my meal might be coming back up.”

”It was your idea, big oaf.”

”I know. I’m really sorry. I promise I won’t have one again.”

And that’s mission accomplished. Senku fiddles with the roasting spits before he offers his hand to Taiju and pulls him back up.

Artificial insemination in stone age conditions sounds like an interesting challenge, and Senku is confident that given enough time, he would be able to figure it out. But it’s hardly something he would be putting into personal use.

-

Taiju snores when he’s on his back.

Senku hasn’t been able to go sleep. He watches his friend, though can’t really see much more in the darkness than a faint outline. He can, at least, make out Taiju’s chest rising and falling in time with the noise he makes.

He remembers the wrenching, unreal feeling he had when he thought that Taiju might never wake up again. It felt like the world was falling in on him from all sides, about to crush him like a bug.

He doesn’t want Taiju to know what that's like. Grossing him out is preferable to that by far.

Chapter Text

”What are you making?”

”What does it look like I’m making?”

Intrigued by the unusually grumpy reply, Taiju squints at the thing in Senku’s hands. He’s holding a stalk of bamboo that’s been slit open and carefully bent at one end to form a flat, wide part with edges that curve up. It looks like an awkward spoon. Something about it looks familiar. He knows he’s seen something like it before. ”Oh, I know! It’s a peeing spoon, isn’t it?”
Senku grimaces. ”Do you have to call it that? That got old ages ago. Its name is stand-to-pee device, or stp device for short.”

”It looks like a spoon and it’s for peeing. So it’s a peeing spoon!”

”It’s really not.”

”Why are you making a peeing spoon, though, Senku? It’s just us here.”

”I’m used to it, I guess.” Senku turns the thing thoughtfully around in his hands. ”It feels strange not to have one when there’s someone else around. And it’s not a peeing spoon.”

”If you say so.”

The conversation hovers at the back of Taiju’s mind, niggling at him. Senku has never before been worried about Taiju seeing his peeing spoon, but now it kind of sounded like he was, for a moment there. He sounded grumpy and stressed. Ever since Taiju found him here in the stone world, Senku has been a lot more grumpy and stressed than usual.

Maybe it's because Senku is stressed about bringing back science, and that’s why he's grumpy about unnecessary things. Taiju’s granddad does that sometimes, too.

That gives him an idea. When Taiju's granddad gets grumpy, his grandmom usually chides him gently and tells him that it's not that serious. He can also help Senku relax by reminding him that Taiju is already familiar with all this. That way, Senku can forget about the little stuff and concentrate on the big things.

-

Taiju develops a verbal tic.

”—your peeing spoon—”

”A peeing spoon—”

”—peeing spoons—”

”—the peeing spoon, Senku.”

Why the hell he is so invested in Senku’s personal equipment all of a sudden, Senku has no idea. Taiju never cared before, but now he won’t stop talking about it. In the span of three days, Senku has found out that it gets really, really tiring to be constantly reminded of your ”peeing spoon”. If this keeps up, he is going to have to do something drastic.

The following morning, Senku climbs down, intending to go to the river to get washed up.

”Don’t forget your peeing spoon!” Taiju yells at him from the tree house.

A proverbial vein goes pop in Senku’s head.

Next time the big oaf is out foraging, Senku cobbles together another device and replaces Taiju’s spoon with it. At dinner, he hands Taiju’s bowl of stew over with the stand-to-pee device sticking out it. Overexposure put him off one bad idea, so having an stp device in his food should curb his fixation on them, too.

Taiju shovels stew happily into his mouth a couple of times before he says, ”Thif feelf odd,” with the device still stuffed in there. He takes it out, looks at it, and then lets out a very loud and satisfying shriek. ”Senku! There’s a peeing spoon in my bowl!”

Senku plucks it from his hand and makes a show of examining it. ”Relax, it’s a brand new one. I made this yesterday.”

”Really? Whew, I totally freaked out for a moment!” Taiju chuckles nervously. ”How did it get in there?”

”Gee, I wonder.” Senku holds it out to Taiju. ”Here.”

Taiju takes it gingerly and holds it between his thumb and index finger. ”So, uh, do you know where my actual spoon is?”

”I don’t keep track of your stuff for you.”

”I must have lost it then. Whoops.” Taiju laughs. ”That was dumb of me.”

There is an empty clay pot in the corner of the tree house, and it has a wooden spoon stashed inside it. Senku feels a bit guilty about it. But not guilty enough. ”Yeah, you should take more care, big oaf.”

”At least I have this thing, then. Otherwise I wouldn’t have a spoon at all and then I would have to drink my dinner.”

”That would be a tragedy, yeah.”

Taiju eyes the stand-to-pee device dubiously. ”It’s kind of weird, you know, eating with a peeing spoon. It’s not even really a spoon, is it? Even if it’s called that.”

Senku does a fist pump in his head. ”That's because it’s not a spoon, and it isn’t called that either, because it isn’t meant to be used as one.”

”I know!” Taiju suddenly exclaims, brandishing the device at Senku. ”I’m going to call this one a peeing spoon spoon! That way I will remember that it’s different from a peeing peeing spoon, so it won’t feel weird to eat with it!”

Senku gapes at him.

Taiju plunges the stp device into his bowl and shovels more stew into his mouth. ”I gotta say, Senku, the peeing spoon spoon works pretty well as a spoon.”

The situation is quickly sliding out of his control. ”Uh, Taiju—”

”Whuh?” Taiju smiles at him with his cheeks puffed out. Then he swallows and holds out to device to Senku. ”Wanna try it?”

The next day, Senku ”accidentally finds” Taiju’s actual spoon, confiscates the unfortunate device and buries it under a rock, because if he never hears the words ”peeing spoon spoon” again, it will be too soon.

Chapter Text

”My face hurts a lot, Senku! That’s not a nice way of shaving.”

”It’s technically not shaving,” Senku says. His shoulders are still heaving. ”Shaving would involve a blade of some sort. That was more like epilation.”

”Yuzuriha told me that epilation is murder! Can’t I use a stone knife instead?”

”If you want to risk nicking yourself, you can.”

”Oh, right. I guess I’ll pass then.”

Senku keeps sniggering at him for the rest of the day. Taiju almost gets mad at him when he does it the fifth time, but then he gets to thinking.

There’s nothing new about Senku having his mind wrapped up in a project, but he's more serious about it here in this stone world. Of course, the project is more serious, too. Even so, Taiju is a little worried about him. This might have been the first time since he woke up that he has heard Senku laugh like that.

Senku could do with some cheering up.

His first few attempts aren't exactly resounding successes. The trees are really uneven and the campfire flickers, so the dinosaur shadow puppet he tries to make eat shadow Senku's head doesn't show up well. Senku looks at him crossly and asks what is the matter with him. The funny spotted fish he catches from the lake makes Senku go on and on about bacterial disease and the threat it poses to their resources. Challenging Senku to see which of them can hop around on one foot the longest ends with Senku staring at him until he slips and falls into a snowbank.

However, Taiju isn't one to give up easily. They’re going to the miracle fluid cave to change out the nitric acid pot when he gets a brilliant idea.

”Senku! We should have a snowball fight!”

The look Senku gives him isn’t promising. ”What are you, five? Why would we have a snowball fight?”

Taiju stops. ”Because it’d be fun!” he insists.

”We have better things to do than play little kids’ games.” Senku keeps walking.

The idea is brilliant, Taiju just needs to get Senku to see that. He bends down, quietly scoops up a handful of snow and packs it into a loose ball. It hits Senku squarely between the shoulder blades and sprays snow all over his back and up his neck.

Senku whips around, eyes wide and nostrils flared.

The second snowball grazes his shoulder. Senku instinctively jerks away from it. His lips start to pull away from his teeth and his fingers curl.

Taiju grins. It's on.

A couple of minutes later, he’s having second thoughts about this.

Senku is generally not that good at sports, but if he gets really worked up about something, he throws himself totally into it and doesn’t back down. That one time in the 3rd grade gym class was a good example. Right now is another one: Taiju has been snowballed in the head four times, while Senku dodges between the trees, so that most of Taiju’s throws miss.

After the sixth snowball clips him on the ear, Taiju changes tactics.

Senku yelps when he is tackled to the ground. Not giving him a chance to recover, Taiju scoops up snow and shoves it straight into Senku’s face. Then he sits back and watches Senku splutter and struggle to sit back up.

Senku’s hair is plastered into his cheeks. He glares with the heat of lava, but the effect is completely ruined by his splotchy face and the drops of water and bits of snow that dribble down his nose and brows. He looks like a cat that got dumped into a bath.

Taiju loses it. He clutches his belly and howls.

Taking his eyes off Senku is a mistake. His collar is suddenly yanked back and icy slush is shoved down his neck. It’s under his coat and on his skin and it’s cold cold freezing cold, he can’t reach it and it’s sliding down his back—

Beside him, Senku stumbles to his feet and runs away. His cackling fades into the distance.

-

After peeling his coat and obi off to get the snow out from underneath, Taiju gets himself back into order. He follows Senku’s footsteps down the familiar path, rubbing his hands together and shivering a little.

He finds Senku a bit of a ways from the cave, already on his way back. Senku has the full clay pot in his hand. ”That was the highest-pitched squeal that I’ve heard in three thousand and seven hundred years,” he tells Taiju smugly by way of greeting.

Senku stays in a good mood for the rest of the evening, so Taiju judges his experiment a success.

Next time, he lobs the snowball right at the back of Senku’s head and takes off.

”I’ll build a snow cannon and bury you alive with it, you goddamn blockhead!” Senku yells as he gives chase and lobs loose handfuls of snow in Taiju’s general direction.

Chapter Text

January is very cold. Taiju and Senku sit on log stumps by the fire late into the night, trying to stay warm.

”It’s your birthday tomorrow,” Taiju says, apropos nothing. ”Do you want to do something to for it?”

Senku stokes the fire with a long stick. ”Nah,” he says. ”I’m more than 3,700 years past being a kid who wants a birthday party.”

-

Next morning, Senku climbs down to get the distillation system going and finds a packed, lumpy mass of snow on his seat. There are twigs and bits of coal sticking out of it.

”What the hell is this?”

”It’s you!” Taiju has followed him to the lab and stands beside him, beaming. ”Well, it’s snow-you. I made it for you before you woke up.”

Senku picks the snow blob up. On closer examination, it turns out to be made of two separate, uneven lumps that have been smashed together. There’s a bigger lump on the bottom and a slightly smaller lump on top. The top one sports a half-circle of coal bits and two larger coal pieces above them. One of the two is bigger and sits higher than the other. It looks a little bit like a smiley face, if you turn your head and squint. Small sticks jut out messily from the top, two slightly bigger ones jut out from its sides, and two tiny ones have been squished in vertically above the coal eyes.

”Thank you. It looks terrible. There’s not even one millimetre of resemblance.” He sets it down on the ground by his seat.

”Aw, Senku—oh, that’s right! I was also going to sing! Happy birthday to you, happy birthday to you—”

”Stop that.”

”—happy biiiiiiiirrrrrtthhhhdaaayyyyy dear Seeeeennkuuuuu—”

”Stop singing, you big oaf!”

”—happybirthdaytoyou!” Taiju finishes in a rush.

Senku crosses his arms and taps his foot. ”Are you done?”

”Yes.”

”Good.”

-

There’s not much to do while Taiju is out fishing. The distillation system needs to be watched, but once the fire is going steadily, it gets pretty boring.

Senku eyes the bumpy little monstrosity next to his seat. Its uneven coal eyes goggle back.

-

Taiju has only just put his catch down when Senku shoves something into his hands.

”What’s this?” Taiju turns the thing around. It consists of three carefully patted-down snowballs of decreasing size, piled on top of each other. The topmost one has been decorated with a smattering of short, upright sticks. For a face, it has two coal bits of almost the exactly same size, and two thick bits of bark above them. For arms, it has two little branches sticking out in front of it, with three twig fingers on one side and two on the other. Instead of a coal mouth, there’s a sizable hole.

”I didn’t get you anything for your birthday, either, so now you get a late ugly snow sculpture. You’re welcome.”

”Aww, Senku! Thanks!” Taiju strides over to where Senku is sitting and plops it down next to the misshapen snow-Senku. ”Now they can be best friends!”

”Hooray.” Senku peers at the fire. ”Go get some more wood, will you? We’re going to run out soon.”

”Will do!”

Taiju returns with a large haul of chopped wood that he starts piling into the groove they dug into the snow bank. The stash is almost empty, so he has to put the new wood far back. The snow on the ground there is not as tamped-down as it is on the path, so when Taiju reaches, his foot slides. He flails, trying to get his balance back, and comes close to kicking the little snowmen.

”Watch it, big oaf!” Senku chides as he reaches down to move them out of the way. ”You almost stepped on us.”

Chapter Text

The distillation set breaks a second time near the end of the winter. They lose about a third of the alcohol they were working with.

It’s not the disaster that Taiju at first thinks it is. After Senku tells him to stop pulling his hair out, he says that all it does is slow them down a little. They don’t even have to wait all year to make more wine because they have dried grapes. This time the pot didn’t even explode on them, just cracked in the middle and left them plenty of time to save the wine inside.

Senku spends a good while scowling at the wreckage, anyway.

”You can make a new one,” Taiju says comfortingly.

”Yeah, once the ground thaws enough. Still, I should store some clay for next winter, in case something like this happens again. I didn’t think to do it before.”

-

Senku looks through his stash in the laboratory to see if he has anything to use to fix clay, and he and accidentally knocks one of the stone swallows off the shelf. It falls on a rock that’s under the shelf and one of its outstretched wings, which already had a crack on it, snaps off.

Senku lifts the pieces onto the table and frowns at them.

”Oh no, it broke!” Taiju peers over his shoulder, concerned. ”Do you think it felt that?”

”I doubt it. Swallows have even less reason to remain conscious for nearly four thousand years than humans do. Plus it might not have felt that even if it was conscious. I didn’t feel the cracks form in my face.”

”I didn’t feel mine, either.” Taiju prods at his own face. ”That’s good, I guess. Do you think we can put it back together?”

”It didn’t work with humans.” Senku turns the pieces around and tries to fit them back together. When he lets go, the little bird falls apart again.

The swallows are really useful, but they’re also alive. Senku has used them for his tests without the slightest hesitation, but he had imagined that once he was done with them, he would just dump nital on the whole bunch and let them go. Now he’s gone and broken one.

He wraps the pieces into a scrap of leather and puts them back on the shelf.

-

Later that day, Senku feels a headache coming on. He climbs up to the tree house to get his jar of willow bark, but when he opens it, a musty smell greets him. He draws a momentary blank on how this has happened, but then he remembers that the last time he used the was the rainy season, right before Taiju was revived. When he had, uh, stress issues. He must have not closed the jar tightly enough, and at some point, water got in. It’s been percolating on the shelf ever since, and now his entire stash of anti-inflammatory painkillers is growing mould.

-

Senku says he's okay, but he is more quiet than usual for the rest of the day. So quiet, in fact, that Taiju checks up on him several times after they've gone to bed. Finally Senku whips around and tells him to leave him the hell alone. He probably needs some space, so Taiju does what he says. Sometimes Senku gets cranky and needs to cool off.

Taiju has started to drift off when he hears rustling. He turns his head towards the noise and sees Senku inch across the straw mat, bringing his blanket with him. He doesn’t look Taiju in the face. He shuffles over until they’re side by side. Once he’s there, he curls into a ball against Taiju’s side and pulls the blanket up to his ears. Taiju turns and throws half of his own blanket over him. He leaves his arm stretched out.

When he was really small, Taiju used to wish he would get a brother. He could never decide between whether he would like a big brother or a little brother, though, and he often wondered what the difference between those would be like.

Senku mumbles something and burrows closer. His hair threatens to get into Taiju’s nose.

He never found out what the difference was between having a little brother and having a big brother. Instead, he now knows what it’s like to have a friend who is usually the big one, and sometimes the little one, but mostly just kind of like a brother.

He’s never told Senku this, but somehow he thinks that Senku knows anyway.

-

Next morning Senku persuades Taiju to help him heat up a large jar of water and carry it to the riverbank, where they dump it on the ground to melt down some clay. It’s a wonder that no one gets scalded.

They wind up with a basket full of runny goop, a broken spade handle, and Senku having to be carried back piggyback because he slipped on the muddy bank and got both of his shoes wet. He holds the basket against Taiju’s chest and grouses most of the way back. By the time they get to the clearing, they’re both wet and messy.

While his shoes dry up, Senku uses the clay to patch up the distillation pot. Once it’s done, it sputters a little, but it works.

”It’s a real slap-dash job and I still have to make another one later,” Senku tells Taiju, ”but now we can finish the distilling and start experimenting with different concentrations without having to wait for the ground to thaw.”

Taiju closes his eyes and clenches a hand into a fist. ”It won’t be long now, Yuzuriha.”

Behind his back, Senku smiles.