Chapter Text
Every time that Senku has to deal with a situation that involves illogical human thinking, he wishes that Gen were here to help him.
It's irrational— Senku knows why Gen isn't here to help him. Gen is somewhere in America, more than eight thousand kilometers across the Pacific Ocean, still trapped in stone. And he's going to stay stone, until Senku can figure out a way to get him.
None of that stops the thought from continuously resurfacing, though.
Because Gen is the balm that soothes his conversations with others. He's the one that's always been able to bridge the gap between science and people in a way Senku never could. The one who he's always been able to count on to talk people into doing what he needs them to do. So every time he reaches a complication, he thinks, if Gen was here, he could have solved this ten billion times faster.
And it's always true. If Gen was here, he would have been able to smoothly integrate the village with the Kingdom of Science. He's certain Gen could have come up with some scheme to unite the two that didn't have to rely on winning the Grand Bout. (And on that note, he is not looking forward to having to explain to his boyfriend that in his absence, he got married and divorced.)
If Gen was here, Senku is certain that he would have been able to manipulate Magma to avoid the multiple attempts he's taken at Senku's life. Kohaku wouldn't have to act as a constant bodyguard for him, and he could actually use her more efficiently in other places.
If Gen was here, when Ukyo was sent by Tsukasa to spy on them, Senku is certain that he could have solved the problem with a single conversation, rather than spending weeks trying to convince him that they had no plans to kill anyone. Even now, he feels like Ukyo is waiting for the other shoe to drop, rather than being a full fledged, cooperating member of the Kingdom of Science.
Hell, he wouldn't even be surprised if he could have figured out some way to talk Tsukasa down before he went on his full statue breaking rampage. Gen has always been able to pull off the seemingly impossible for him.
In short, his life would be much easier if he had his mentalist here with him. And it has nothing to do with the fact that he misses him. Because missing Gen is not productive.
Gen's presence would be indispensable in this stone world. Understanding the complicated, illogical thinking that contributes to the logic of the human brain would be invaluable, and if Gen was here, he would be able to easily understand and untangle it for him. He could always understand things like that when Senku couldn't.
So usually, while wishing for Gen's presence is illogical, he's able to justify that it's for entirely practical reasons. It's like when he spots moments of inefficiency, and his brain reminds him of how much quicker it could be, if he had the proper manpower.
But right now, Senku can't even lie to himself and say that he wishes that Gen was here for entirely practical reasons.
Really, he just wishes that his boyfriend was here, because he'd know exactly what to say as Senku is confronted with the fact that Byakuya has been dead for thousands of years.
He'd know just how to squeeze his hand, how to move closer, but not too close— he'd know exactly what Senku needed before Senku knew it himself.
Byakuya would have died eventually, Senku tries to rationalize with himself. Even if he was petrified, the reality of life is that eventually, the cessation of all biological functions that sustain living organisms will follow. Even if he had never gone to space, or was petrified in space, or petrified upon landing back in the atmosphere, Senku would have had to deal with his loss at some point in his life. Even if the petrification hadn't happened at all, Byakuya would have died one day. He tries to convince himself that the outcome wouldn't have changed— but it has.
Because he didn't get to say goodbye.
His last conversation with Byakuya was the morning before he was petrified, and it only happened because Gen basically strong armed him into calling Byakuya. They didn't talk about anything that mattered. He couldn't have known it would have been the last time they spoke.
Senku didn't even say goodbye. His chest still aches with the loss. It already hurts so much, it's not worth it to go through what-if scenarios about what could be. It would be much more logical to accept things as they are, and stop wishing for hypotheticals.
But he can't stop himself from thinking about Gen anyways, and wishing that he was here to help him figure this out. Tell him the right words, do the exact right thing, and help him figure out what to say to Ruri as she leads him away to tell him the last message from his dad.
"Senku, what's up," Ruri recites as she leads him. Her voice is conversational, as if she's talking about something ordinary like weather, and not Byakuya's last words. Although, it probably is ordinary for her. She's heard this recited enough to memorize it.
He privately squirms at the grand scale of 3,700 years, and how many people have probably heard his dad's words for him, passed down through generations.
He hopes that Byakuya didn't say anything embarrassing.
He steps carefully over the tree roots, making sure he doesn't trip in the dark as Ruri leads them further. "If you're hearing this story right now, it'll probably be thousands of years from now. But that means you've broken out of the stone, right?" Senku's chest tightens at his dad's unwavering belief in him.
"I'm doing great, by the way! Well, not really. I'm definitely dead by then." Ruri pauses after this, glancing back at him as if to gauge his reaction. Senku doesn't let his face twist. The idea of showing emotion in front of Ruri, in front of anyone, makes him want to peel his own skin off.
(Gen would have noticed him doing it immediately if he was here, and would force him to talk through what he's feeling. But Gen's not here, so here he is, pushing it down.)
Instead, he keeps his face straight, and nods for her to continue. Her eyes tighten, but she continues.
"Here are your souvenirs, just like I promised. Some people you can call friends, all tied together by the one hundred tales!" They round the bend, and Senku takes in a sharp breath.
"The post apocalyptic world was pretty fun, even if some stupid pneumonia got us in the end. But with your science, Senku, and the strength of everyone you can count on, I know you'll make the world a fun place again," Ruri says. Senku listens raptly, even as he takes in the scenery.
The forest has opened to to expose a hill, sitting in an almost bowl-like valley, with more gravestones lined here than he can count. They climb the mountain in rows. Hundreds of markers of lives lived— a vast reminder of the years that have passed. Senku cranks his neck up, trying to properly take in the scale, but the graves vanish under the bright silver moonlight.
Somewhere, on this hill, lies Byakuya's grave.
"No man is an island, right? There's no way you're alone! Not only will you have the village, I know you'll figure out a way to bring Taiju, Yuzuriha, and Gen back. And tell them I say hi when you do!" Senku can't hide his reaction then— he feels the way his heart jumps at the reminder of Gen, and his brows pinch painfully. Ruri sees it— he knows she does, but he's endlessly grateful that she doesn't ask questions. "I've seen the way you rely on the three of them. With your strength combined, I know you won't lose this fight! Build civilization up from scratch, and save all of humanity! I know you can do it, Senku!"
He waits for his heart to still, and Ruri waits patiently. "That's the end of the hundredth story," she says. "This is the village graveyard. And up here…" she leads him up the hill, and he follows, until they reach the peak. "This small grave marker was brought on behalf of our founders."
She produces a flower from somewhere underneath her robes. For one ridiculous moment, Senku sees Gen pulling out flowers from his sleeves for his performances or for a dramatic flair, and immediately abandons that train of thought. She brings herself down to a crouch, and lays the flower on the dirt in front of the grave.
Byakuya is gone. Taiju and Yuzuriha are working as spies in Tsukasa's empire. Gen is in America, trapped in stone. Senku may have recruited a village, full of people willing to help him, but he still feels completely alone.
"You don't have to answer this," Ruri says after a moment. "But I am curious. I recognize the names Taiju and Yuzuriha. Kohaku told me they're working as spies with the long haired man who killed you." She pauses, as if gathering her words. "But who is Gen?"
After Ruri asks that, her face immediately twists with sympathy. Senku knows he must have an ugly expression on his face, one that caused her to look at him like that, but he can't find it in him to smooth it out.
"He's…" He hesitates. My partner in crime. One of the most important people to me. The most annoying, yet useful person I've ever met. "…still stone. And I won't be able to bring him back for a long time. But I will," he promises, mostly to himself. "I'll bring him back. I'll bring everyone back. All seven billion people."
Ruri stands from her crouching position gracefully. "If anyone can do it, I know you can, Senku. You've already done so many amazing things. Things we never could have dreamed of seeing." She turns. "I'm going to head back to the village. Take all the time you need."
He stands, expressionless, as he hears Ruri's footsteps signifying her departure grow quieter and quieter. Once she leaves, he finally sits, and thinks.
"Hey dad," he finally rasps out. "I…" And despite himself, a tear runs down his cheek.
He clenches his jaw, wiping it away roughly. He hates this. He hates dealing with these illogical, messy feelings. Crying doesn't ever change anything— it won't bring Byakuya back, and it won't get Gen out of stone. Another tear follows, and he presses the palms of his hands against his eyes for a moment, before taking a long, composing, breath, willing the feelings away.
"Thanks for the souvenirs. If it wasn't for them, I might actually be struggling." His throat tightens. "I… dad, I miss him. I miss you. Things would be so much easier if you were both here in Japan, and I could revive you both." He chuckles. "Although, without your science souvenirs, I'd probably have died already, huh?" he says wryly.
Then, with just the moon to keep him company, he talks to the memory of his father. By the end of it, he's much more confident.
Because now, he has a road map. He's going to defeat Tsukasa, and recruit the Empire of Might to his cause. And then when he has a bigger work force, their first job is going to be to build a boat and go to America. The source of the petrification was South America, which he knows because that's where the stone birds were first spotted, which means that eventually, they'll need to go there. But a more pressing concern is where to get the supply of alcohol needed to revive everyone. Nitric acid is easy to make if you have rhodium or platinum, and Senku has a hunch about platinum that he plans to follow up on later.
But alcohol is the real issue. He needs a plant with a high enough sugar content to actually produce alcohol, and it needs to be something he can grow in bulk.
The last time that Senku talked to to Gen, the evening before the petrification, he was in San Francisco for a show.
And in California, just north of San Francisco you have an ideal spot for growing dent corn— a stupidly easy corn to grow, with a stupidly high sugar content. If Senku plans to revive all of humanity, he needs to secure a plant capable of producing massive amounts of alcohol, and yellow dent corn is one of the best ones he could ask for.
Senku needs to get to California to advance science further, and he needs to get to California to get to Gen. It's practical, and completely doable.
"You're right, dad," he calls out as he prepares to leave. "I need to get Taiju and Yuzuriha back." He pauses. "And I need to get Gen back, too. No matter what it takes."
He turns to leave, and a sentimental part of him imagines his father is looking down at him from the moon, proud.
Senku's regular spot to experiment at the park was chosen for one reason — it's far enough away not to be bothered.
The playground is on the opposite side of the field, and right here next to the river, the most activity you see are old grannies and people walking their dogs. No one that would pay attention to him, which is just how he likes it.
Right now, he's trying to test something that he read in one of his chemistry books— making thermite. Thermite can be made by mixing aluminum powder with iron, and it's stupidly useful. When you mix the two together, and ignite it, the reaction can get hot enough to even melt steel.
Senku has some iron sand to test it with, but he doesn't have aluminum powder. That means that he needs to improvise, which is easy enough. He has both aluminum foil and a mortar and pestle, and he figures if he grinds it long enough, he can get some powder out of it.
It takes a while, and it's incredibly tedious— he's already been grinding the aluminum pieces into finer and finer bits for nearly thirty minutes. But science doesn't care about how boring or tedious something is: what's important is the result. So he sits there, and meticulously grinds the aluminum under his pestle.
He's doing just that, repeating the process, when he hears footsteps behind him. He doesn't bother looking— it's probably just someone passing by. Nothing worth checking out.
"What are you doing?" a voice suddenly asks.
Senku looks back to meet it, to see a boy with strange, dual colored hair. A large patch of white sits in the middle of his black hair, splitting it neatly into two, and Senku can't help but stare at it.
"Your hair is weird," he says in response, vocalizing his thought.
The boy immediately frowns. "Hey, that's mean. You have weird hair too, but I didn't tell you that."
"It's not meant to be mean," Senku replies.
The boy crosses his arms. "It's still mean, though."
"It's not," Senku insists. "It's an observable fact. Your hair is outside what most people would consider the norm. It's not a bad thing, though. Outliers are expected to exist, and ignoring them can lead to incorrect data and assumptions."
The boy stares, his earlier offended expression turning dumbfounded. Senku only recognizes it because of how many times Byakuya has laughed about it— especially after he talks to adults about his plans to go to space in depth. He turns back to his mortar and pestle.
"Huh. You're really smart," the boy says. "And you still haven't told me what you're doing."
"Oh. Well, right now I'm trying to make aluminum powder. Once I get a usable powder form out of this stuff, I can combine it with my iron sand over there and heat it up for a wickedly cool reaction."
The boy lets out a hum, and sits down cross-legged next to him. "Can I watch?" he asks.
Senku glances over. "Yeah, but once I start heating it up, you'll need to stand back. It'll get dangerous."
The boy eyes him. "If it's dangerous, why are you doing it?"
Senku grins. "Because it's cool." He looks back down. "And I need to learn everything I can about science, so that I can go to space."
The boy giggles. "Uh, we're kids. Kids can't go to space."
Senku rolls his eyes. "Yeah, duh. I'm not old enough to qualify for the astronaut trials, and I'm not even one millimeter athletic enough to pass them, either. So I'm building a rocket so I can take myself, obviously. That's why I need to learn everything I can."
The boy laughs harder. "You're so weird," he says. Senku hears that a lot— people at school call him weird, and he hears adults mutter about how he's a strange child all the time. But this doesn't feel like that— instead, it feels more like when Byakuya calls him a weird kid, in that tone where his voice physically sounds like a smile.
They sit in silence, for a bit, The boy watching Senku grind the aluminum foil further. He's strange— none of his classmates ever showed this much interest in his experiments. It reminds him again of Byakuya, the only one who's taken him seriously.
Senku puts down his tools again. "What's your name?"
The boy blinks. "Asagiri Gen. What's yours?"
"Ishigami Senku. Want to be my lab assistant?"
Gen stares for a second, then he smiles. "Sure! What's a lab assistant?"
"It's like a helper. You'll have to come over here after school every day to help me with my experiments."
"That sounds important."
Senku nods seriously. "It is."
Gen looks amused as he tilts his head to the side. "That also sounds like hanging out with a friend."
Senku looks him up and down and considers. "If it means you'll help me out, then sure."
He beams. "Okay! What should I do first?"
Senku hands over the mortar and pestle. Science may not care about whether something is boring or tedious, but Senku finds that he starts to care once he has a willing test subject to lighten the load.
And Gen complains a bit, but once Senku shows him the way that the aluminum and iron sparkle and light up like fireworks when he heats them up, his eyes light up and he's cheering.
Senku stares at Gen. The way that his eyes crinkle around the edges makes something that feels like the satisfaction of an experiment finally succeeding sit warm between his ribs.