Chapter Text
Death is so strange.
The best way Byakuya can describe it is that he's finally, completely present. There are no wandering thoughts, no aches in his knees, no hunger, no exhaustion tugging at the edges of his mind. Every moment is experienced fully, without distraction. At the same time, he can somehow see countless branching possibilities stretching away from the living world, every choice giving birth to another.
Time doesn't seem to exist here, or maybe it exists differently. He can't feel it passing anymore - there are no mornings or evenings unless he wants there to be, no seasons unless he remembers them into being. Entropy has no grip on this place. Nothing ages, nothing decays. It simply is.
And yet he can still see the world beyond it.
Thousands of years slide past on Earth as easily as clouds drifting across the sky. Cities crumble one wall at a time until they become hills beneath forests. Steel rusts away. Glass clouds over and shatters. Highways split apart as roots force themselves through the pavement, weeds filling every crack before great trees follow after them. Apartment towers collapse floor by floor, swallowed by vines and moss until it becomes difficult to tell they had ever been built by human hands at all.
The air changes too. Carbon dioxide and methane slowly leave the atmosphere. The ice sheets creep south again, glaciers grinding patiently across mountains that had once been bare. Forest fires sweep through continents before new green pushes up from the ash. Rivers change course. Coastlines shift. Coral reefs die in one age and new ones bloom in another.
Animals spread into the empty places people left behind. Dogs forget what humans ever were; wolves reclaim old territories. Bears wander through abandoned suburbs. Whales cross oceans that no longer echo with cargo ships. Birds nest in the hollow skeletons of skyscrapers until those finally collapse into the earth.
An earthquake tears open what had once been the western coast of the United States, mountains buckling and coastlines reshaping. A volcano that people had once called Mount Vesuvius erupts again, ash climbing into the sky while forests farther down the slopes disappear beneath lava. Hurricanes come and go. New islands rise from the sea. Others disappear beneath it as the sea level rises.
Humanity had once thought itself permanent, but the Earth had never agreed. It’s almost beautiful, watching nature reclaim the world.
Far away, on the little island where the Soyuz landed, life continues. The children of the astronauts are parents, and then grandparents, and then they die. Faces Byakuya had known as toddlers wrinkle with age before vanishing in turn. New babies are born with familiar smiles and unfamiliar eyes. The Hundred Tales are told beside evening fires by people who have never seen electricity, who can't imagine trains or airplanes except as half-mythical things from stories.
The Hundred Tales stay the same. He had hoped they would - he needed them to. They have lessons, they have advice, they have guidance. They’re meant to help the children of the astronauts survive.
But the Tales were also meant to survive across the eons, to reach the ears of Senku. He’ll be back one day; Byakuya knows it. It’s as inevitable as the sunrise that Senku will again walk the earth.
There are pathways through this strange place after death, though Byakuya doesn't really know where they lead. He sometimes sees people passing along them, brief glimpses of strangers and familiar faces alike before they disappear around bends he can't follow. Nobody seems frightened. Everyone simply continues onward when it's their time.
When Byakuya died, he ended up somewhere that, for lack of a better word, he thinks of as heaven. Sometimes he's back in the little apartment in Tokyo that he shared with Senku - the one with the cluttered kitchen, the yellow curtains in the front room, and the bathroom door that used to stick if you actually took a bath because it would cause the door to swell in its frame. The balcony is warm in the evening, and if he leans against the railing he can almost hear traffic drifting up from the streets below. The telescope in Senku’s bedroom still points toward the sky.
Other times he's on the island again, with its huts and gardens and the sparkling expanse of the sea. Nets dry on wooden posts beside the beach while seabirds circle overhead. The ocean rolls in, waves hissing softly across the sand before pulling back again. The graves of his friends aren't there - this island remembers only the good parts.
People have picked different paths. Shamil and Connie become part of the universe itself. Their souls spread outward until they are impossible to separate from starlight and gravity and the quiet spaces between galaxies. Byakuya likes imagining them scattered among the constellations they once looked at through the Cupola windows aboard the ISS. Darya and Yakov have their own little corner of this peaceful heaven-like place in the home they must have shared in Russia; Byakuya sometimes sees them. Byakuya’s mother chose Nirvana, the merging with the cosmic whole. Byakuya’s father picked nothingness; his essence is gone.
Ren and Konomi had chosen reincarnation, though Byakuya suspects their motives were different.
And for a while, Lilian is there with him, sharing their island heaven, as golden and as beautiful as he’ll always remember her. They’re not always around each other, but when they are, it’s as warm and electric as it has always been to be near her. They watch their children and their grandchildren grow up, and die, and make their own way through this space after life - choosing heaven or to be a ghost or stranger things besides.
"I want to go back," Lilian says eventually. They're standing on the beach, watching the sun settle toward the horizon. The light turns the water bronze, then gold, while a warm breeze stirs her hair. Sebastian is wandering through the tide pools.
It's not really a surprise, although it is sad. She died so young. There had been concerts she never got to sing, countries she'd never visited, songs she'd never written. She'd watched their children and grandchildren live full lives from this place out of time, watched them laugh and fall in love and become old, despite barely having gotten to do that herself.
"I think I could be part of it again," she says quietly. "Despite the pain...it was a beautiful thing, being alive. I want more of that."
Byakuya looks at her for a long moment. The lines of hardship are gone from her face, and so are the calluses she'd earned on the island. She's simply Lilian, all the versions of herself existing at once - the little girl singing to keep her spirits up, the pop star, the astronaut, the survivor, the love of Byakuya’s life.
He smiles, his heart so full of love it almost aches - he knows what this means. He'll never see her again exactly as she is now, as Lilian Weinberg.
Her soul will become something new. Maybe she'll be born as one of their own descendants centuries from now. Maybe she'll become someone living on another continent entirely one day, when the world is revived. Maybe she'll come back as a tree rooted on a mountainside, or a fish drifting through the deep sea, or a child who'll grow up loving music without ever knowing why. She’ll be there, within it - not unchanged, but added to, like a coral reef being formed over millions of years, like a star going supernova and seeding the universe with new elements.
"I'll miss you," he tells her. "And I'll always love you."
She nods, because she knows he’s staying - he’ll stay as long as he needs to, as long as he has to, to see Senku again. It’s all he wants - he has to see Senku as himself, as the version Senku knew. He wants to tell his son he loves him, even if he has to wait until the end of time.
She steps closer and wraps her arms around him. He holds her tightly, feeling the warmth of her one last time as the waves curl around their feet. Then she leans up and kisses him, slow and familiar, before resting her forehead against his for a quiet moment.
Neither of them cries. It’s sad, and it’s not. It’s the way of things, to love someone and let them go, and he will always love her, which is why he understands this is what she needs.
Finally, she smiles at him - that bright, fearless smile that first made him wonder how anyone could remain so kind after the end of the world - then she turns toward the sea. She walks forward without hesitation, the water climbing from her ankles to her knees, then her waist. The sunset wraps her in gold until it's impossible to tell where the light ends and she begins.
She keeps walking, and then she's gone. The waves crash onto the shore.
He’s alone now, just himself and the universe.
Byakuya settles back in to wait.
✩₊˚.⋆☾⋆⁺₊✧
He knows the instant the stone cracks and Senku returns to the world - he has the feeling of one of those branching futures finally collapsing into reality, an inevitability becoming truth. It rushes through everything around him, and for one suspended moment he can only stand there, overwhelmed with relief.
His little boy made it. Senku’s alive and breathing again.
His heart aches as he watches Senku squint against sunlight that hasn't touched his eyes in thousands of years. His clothes are long gone, the stone shell breaking away in heavy chunks around his feet, moss and vines sliding off with it. The forest is verdant and green, nothing like the parks and carefully managed trees around Tokyo. Birds scatter at the sound of the stone breaking.
There are humans alive now - his descendents, some of whom came all the way to Japan. Byakuya knows that much. He also knows Senku isn't likely to find them anytime soon - they’re too far away, and Senku has no reason to think there’s anyone else out there but him.
It's Senku versus the world, and Byakuya will put good odds on Senku.
He watches Senku sit up, rubbing at one wrist where flakes of stone still cling to his skin before looking down at the shattered shell around him. His expression settles into that familiar look of concentration Byakuya remembers from childhood, the one that always meant Senku's brain was already several steps ahead. Instead of panicking, Senku studies the thickness of the stone, turns over broken fragments in his hands, examines the surrounding forest, and starts building a plan before he's even fully stood up.
Byakuya knows there has to be fear somewhere beneath all that composure. Senku has always felt things deeply, even if he hated letting anyone see it. He has to be wondering where Taiju and Yuzuriha are, whether anyone else survived, whether Byakuya ever made it home from the International Space Station - if the petrification even went that far.
He doesn't waste time asking questions he can't answer. Instead he gets to work. Senku’s also always been imminently practical.
Byakuya watches him dig Taiju out of the ground with desperate determination, refusing to give up even when his hands blister and his shoulders ache from swinging makeshift tools. He follows clues that nobody else would have noticed, tracing the strange patterns left behind by the nitric acid cave and slowly assembling pieces of a puzzle thousands of years old. Every answer only leads to another question, but that has never discouraged Senku before.
It's slow, uncomfortable work. Senku's constantly tired. He hauls firewood, gathers food, repairs his shelter after storms, and then spends whatever energy he has left chasing scientific answers. By the end of most days he's dirty from head to toe, scratches crisscrossing his arms and legs, fingers calloused and raw. Sometimes he falls asleep almost the instant he lies down.
He gets up the next morning and starts again - over and over, again and again. Senku’s never been one to quit. It’s fascinating, really, the depths of his resilience, his drive to understand and solve the problem in front of him.
The interesting thing isn't really Senku, though - it’s the nature spirits, noticing him almost immediately.
Tiny spirits peek curiously from inside tree trunks, bark opening just enough for bright eyes to watch him pass before sealing shut again. Flower spirits rise from patches of wild blossoms, drifting after him like curious children. The water spirits of the stream watches from beneath the surface while dragonflies skim over the water. The wind spirits dart around him in quick circles, tugging experimentally at the unruly white-and-green hair that somehow survived the petrification looking exactly as messy as always.
They're fascinated - human beings have come and gone over the thousands of years, but none of them have been quite like this one. He’s alone, for one. He’s not particularly strong, and is very reliant on tools. The moment he’s set up with shelter, clothes, and used to the work of food, he immediately starts trying to solve the petrification. He digs up Taiju, he finds the cave with the nitric acid, and starts putting together the dots. It’s fascinating. It’s slow, hard, uncomfortable work. Senku’s constantly exhausted, working himself to the bone just to keep going.
And yet he keeps solving every problem the world throws at him.
The spirits seem to love it, and take it as a challenge. Mushrooms cluster in damp spaces, waiting for Senku to find them. Fish linger a heartbeat too long in shallow water before darting away. Fruit drops from branches just after he looks up in frustration.
They don’t really make it easier for him, though - the spirits love to irritate him. A branch drops squarely onto his head when he's carrying an armful of firewood. The wind changes direction at exactly the wrong moment while he's trying to start a fire. Rain arrives half an hour earlier than it should, soaking the shelter he'd almost finished. Vines snag around his ankles when he's in too much of a hurry. Once, a squirrel steals something he'd been carefully carving and chatters triumphantly from the top of a tree while Senku glares up at it.
Nature delights in challenging him, in irritating the hell out of him.
And Senku just adapts. He changes the shelter design after the rainstorm, he stores food differently after the squirrel. He’s more aware of branches, warier of flooding, sets up barriers to stop the wind from blowing out his campfires.
The spirits never get bored. There’s always something new and entertaining about him, something new to give him, some minor irritant they can cause.
It’s amusing, really. The world bends just the littlest bit to make sure Senku can survive, in ways that would be suspicious if Senku wasn’t a city kid who didn’t really go camping. He’s aware of the challenges of survival, but he’s not aware of what the spirits are doing. Senku will never assume magic exists, will never assume the spirits are there.
He'll spend years working to fit everything into his scientific before he'll ever believe a root purposefully tripped him up, because the spirits thought it would be funny. And somehow, that only seems to make the spirits like him more.
✩₊˚.⋆☾⋆⁺₊✧
Senku's never been someone people can be neutral about. They either love him, want to use him, or hate him. He's too blunt to be universally likable, too kind to be truly cold, and too stubborn to hide either of those things for very long. He'll admit someone else is smarter than him in a particular field without bruising his own ego for even a second, then turn around and confidently explain a concept nobody else in the room can follow. He's difficult to pin down, and people tend to respond to that uncertainty with some extreme emotion.
Death hasn't given Byakuya the ability to read minds exactly - people's thoughts are still their own. But emotions are different. He understands them now in a way he never could while he was alive. Feelings ripple outward, brushing against everything around them. Sometimes they're quiet enough to barely notice. Sometimes they're so overwhelming they color the entire world.
Shishio Tsukasa's feelings toward Senku are like standing too close to a bonfire.
The first time they meet, Byakuya can barely look anywhere else. Taiju’s excited because he’s always admired Tsukasa. Senku’s a little wary of Tsukasa’s strength, and he doesn’t like being forced into making a choice without having any time to think it through. Tsukasa stands in the clearing with easy confidence, broad shoulders relaxed despite the lion lying dead nearby, his expression calm enough that most people would probably think him gentle.
Inside Tsukasa, though, everything is in conflict.
He admires Senku almost immediately; the respect is genuine. Senku is useful, astonishingly intelligent, someone capable of dragging humanity back from extinction through science alone. Tsukasa understands exactly how extraordinary that is.
At the same time, he hates what that intelligence represents. Beneath the admiration is resentment so old it's become part of who he is - anger at wealthy adults, anger at systems that crushed people for being poor, anger at a civilization that let children suffer while others accumulated more than they could ever need. He looks at Senku and sees all the machinery of the old world waiting to come back.
Loneliness runs underneath all of it. Byakuya feels it every time Tsukasa watches Senku and Taiju together - the easy way Taiju trusts him without reservation, the years of friendship already built between them. Tsukasa envies it more than he'd ever admit aloud. Somewhere inside him is the lonely middle-school boy who learned that strength was the only reliable thing in the world - his intellect was never going to get him what he needed, and his compassion was a weakness.
Byakuya isn't omniscient. Death doesn't grant that. He can't see every future, only possibilities branching outward from every choice the living make. Most disappear almost as quickly as they form. Others grow stronger the more people commit to them.
The futures surrounding Tsukasa narrow with frightening speed. Again and again they end with Senku dead.
Tsukasa doesn’t enjoy the thought of killing Senku; he’s at his core someone who is kind, but that kindness has warped, developed sharp edges, tainted by the pain he carries. Every version of his future carries grief with it, and painful regret. He’s filled with the awful certainty that there simply isn't another way. As Tsukasa sees it, Senku will never abandon science. Science will always rebuild civilization. Civilization will always recreate exploitation, greed, inequality, and suffering. If that's true, then Senku has to die before he can rebuild the world. It's horrifying because Tsukasa genuinely believes he's protecting humanity.
Byakuya finds him tragic more than anything else. Tsukasa is brilliant. He notices patterns quickly, reads people well, survives in ways almost nobody else could. But there's so much grief and rage packed inside him that he can only imagine history repeating itself. The old world becomes destiny instead of the past; Tsukasa can only see the pain it inflicted, and he can only see the horrors if it arises again.
There was never anything inevitable about capitalism, or colonialism, or racism, or misogyny, or environmental destruction. They were systems people built, and systems people could have dismantled.
Byakuya wants to shake him. If Tsukasa had stayed beside Senku instead of opposing him, instead of killing him, he could've helped build a world where those things never returned. He understood poverty in ways Senku didn't. He understood exploitation, violence, and abandonment firsthand. Senku would've listened. He always listened when someone could show him evidence he'd overlooked.
Instead, Tsukasa retreats into something simpler. He romanticizes a world that never really existed, imagining humanity at its purest before civilization complicated everything. Nature becomes inherently good. Knowledge becomes inherently dangerous. Science becomes the first domino in every human tragedy.
The noble savage myth wraps around him so tightly that he mistakes it for truth. Tsukasa views civilization as a cancer - and Senku wants to revive science and rebuild the world, therefore, he must be eradicated.
There are so many pathways, but they narrow and narrow until Tsukasa murdering Senku is an inevitability. Senku never got rid of the stone on the back of his neck, and that’s what saves him when Tsukasa breaks his neck.
Because Senku’s not fully dead, he can’t materialize in this world outside of time, beyond death. His spirit hangs there instead, faint and translucent, separated from Byakuya by something invisible but absolute. It's like looking through thick glass. Senku stands there without really standing, eyes unfocused, unable to see or hear him.
The pathways shimmer around him, and most of them still lead back toward life. The stone on the back of Senku's neck is enough. Life isn't finished with him yet.
Byakuya knows the odds are good, but it doesn't matter. Senku’s his little boy, and someone just tried to kill him. He wants to pull Senku into his arms the way he did when he was little. He wants to tell him everything will be okay, that Dad's here, that nobody gets to hurt his son ever again.
Instead, all he can do is speak into the silence, hoping something crosses whatever impossible distance separates the living from the dead.
"You'll be okay, kiddo."
He doesn't know whether Senku hears him, if anything makes it through the distance between them.
Back in the living world, Taiju refuses to accept what he's seeing. Yuzuriha kneels beside Senku with shaking hands, tears streaming down her face as she searches desperately for anything they might have missed. Between the two of them, they know Senku too well to stop looking. He’d go into this with a plan; Senku’s not the type to take an ultimatum. Taiju remembers the fragment of stone still clinging to the back of Senku's neck. Yuzuriha reaches for the revival fluid without hesitation.
Byakuya watches them work, relief and joy surging through them as Senku heaves in a new breath and his red eyes come back into sharp focus.
Thank goodness.
Thank goodness Senku has people who love him enough to refuse to let him go.
✩₊˚.⋆☾⋆⁺₊✧
Maybe Gen doesn't see it this way, but Byakuya thinks Gen fell in love with Senku right from the start, before they ever actually met.
As the stone cracks off Gen and he stumbles, disoriented, into the light, Byakuya gets flashes of what he’s feeling, what he’s thinking, the weight of Gen’s past and all his secrets. The sadness Gen carried makes much more sense now, he thinks as Gen immediately clamps down on the nature spirits and begins strategizing about how he’s going to survive.
When Tsukasa looms over him, a massive and intimidating figure amidst the primitive forest, Byakuya feels Gen’s terror at the declaration that he was revived for a specific purpose. That sharp fear immediately melts into a sweeping wave of relief the second Tsukasa clarifies he only needs Gen for his skills as a mentalist.
Huh. Who would have thought Asagiri Gen was not only actually magic, but also indigenous?
Senku had never cared about his history - he was always confident in who he was and who he built himself to be. He saw himself as part of the legacy of scientists, as Byakuya’s kid, as Taiju’s friend, more than he viewed himself as Japanese or a guy or almost anything else. Senku had always thought he was who he made himself. Maybe that confidence came from knowing the answers were there if he ever wanted them. His parentage wasn't a mystery, and his history had never been something he was forced to hide. He'd always known that Byakuya would tell him the truth if he asked, and it wouldn't change anything.
Gen’s different. He cares a lot about being Ainu, and he’s angry and frustrated that something he views as a part of him can’t be visible for the sake of his reputation. He’s terrified of disappointing his grandmother with his own cowardice and ignorance about their heritage. He’s frustrated his mother is so reactive when it comes up at all. He’s upset that something like his blood has to be a secret at all.
And he genuinely loves the spirits and his ability to speak to them. It's not just that they help him find food or warn him about danger. Every time he interacts with them, he's reminded that the world is bigger and stranger than most people realize. There is comfort in knowing he isn't walking through it alone, that the forests and rivers answer when he speaks, that something deeper and vaster and wilder exists alongside humanity whether anyone else believes in them or not.
Senku doesn’t care about his history, but Gen clearly wishes he could care about his without it destroying his future.
Byakuya watches as Tsukasa brings Gen to the tree that Senku had carved the date onto when he broke out of the stone, all alone. Gen traces the carved numbers, whispering to the spirits to tell him what they could. Byakuya watches as the tree spirit steps out of the trunk, brushing its arm against Gen.
Byakuya can clearly see the image the spirit passes to Gen. It shows Senku, standing alone in the untamed wilderness, carving the date into the rough bark. His face is set in fierce determination, his sharp eyes narrowed against the reality of the stone world. It is an image of Senku challenging the entire world all by himself, entirely unbothered by the insurmountable odds stacked against him.
Gen takes a slow, shaky inhale, a remarkably soft sound in the quiet forest. That is the moment, Byakuya could swear it on his own life.
That is the moment Asagiri Gen fell in love with Ishigami Senku.
✩₊˚.⋆☾⋆⁺₊✧
And somehow Senku doesn’t botch it when meeting Gen, which is maybe the surprising part because he more or less immediately makes Gen perform a lot of physical labor. The bellows for the furnace look painful; Gen is drenched in sweat and exhausted, but he doesn’t leave.
Byakuya can tell that Gen immediately understands he doesn't have a chance if he stays with Tsukasa. Tsukasa values him because he's useful, but usefulness only lasts as long as someone stronger decides it does. Here, for the first time since waking up, Gen can see a future that stretches farther than tomorrow. He doesn't think Gen realizes he's already lost his heart to Senku. He recognizes that the spirits love Senku - the tree spirits peeking around trunks after he walks past, the wind spirits darting through his hair - but he can't bring himself to recognize his own interest.
Senku’s not as rude to Gen as Byakuya feared he would be. Senku really didn’t have a high opinion of Gen’s work, and he’s always really only been polite if he thinks he can get something out of it, but he mostly just makes Gen pump the bellows as repayment for the ramen and then asks about Taiju and Yuzuriha. Gen is obviously a spy. Senku obviously knows he's a spy. Neither of them bothers dancing around it because there are bigger problems than pretending otherwise.
The interesting part is that Senku likes Gen more than he expected to, right from the jump. Senku’s not the type to fall in love immediately, but Byakuya knows him well enough to know he’s intrigued by Gen in their first meeting.
Byakuya recognizes that look - curiosity has always been the fastest way into Senku's good graces. Gen's contradictory in ways that don't make sense at first glance. He's a liar who's remarkably honest about being a liar. He'll admit without hesitation that he's manipulative, cowardly, lazy when he can get away with it, perfectly willing to save his own skin. Then, just as naturally, he'll redirect attention away from every generous thing he does. He talks down his own strengths as easily as he advertises his weaknesses. Every answer is true without being complete. Every joke slides sideways before anyone can ask the obvious follow-up question. Senku notices almost immediately that Gen is protecting parts of himself, and instead of being put off by it, he starts trying to figure out why.
Gen, meanwhile, can't even admit to himself what's happening. He's spent too much of his life keeping everyone at arm's length. Secrets have kept him alive. His heritage, his connection to the spirits, the complicated relationship he has with his mother, the fear of disappointing his grandmother - all of it has taught him that there are pieces of himself it's safer not to reveal. And he immediately recognizes that while he won’t ever hurt Senku, he can’t trust Senku not to hurt him.
Gen’s got his work cut out for him, falling in love with Senku.
Yet fall in love with Senku, Gen does. Byakuya watches it happen the way someone might watch a tree leaf out in spring. It grows quietly, almost invisibly, until one day it's impossible to imagine it wasn't there all along. It settles beside Gen's connection to the spirits and beside the quiet pride he slowly begins reclaiming in being Ainu. All the things Gen had convinced himself he could never keep - love, belonging, a future where he doesn't have to hide every piece of himself - begin taking root together.
It grows through conversations while gathering firewood and teasing remarks traded over campfires, through Senku making Gen cola, through watching Senku trust Ukyo despite every logical reason not to. It grows through nights spent planning impossible inventions and bloodless victories, through the observatory rising piece by piece against the sky, through oil fields and ships and maps spread across tables. It grows every time Gen catches another glimpse of the loneliness Senku hides beneath relentless confidence, every time he realizes that beneath Senku’s bravado and sharp tongue, he’s maybe even more human than the rest of them.
By the time Gen walks into the ocean and asks it for help, it's already written through every choice he makes. He can find information no one else can. He can keep Senku safe. He can help Senku meet his goals, because it benefits Gen if society is restored, because he doesn’t want to be petrified again.
Those things are all true.
They're just not the whole truth.
When Gen slips into that trance with seawater lapping around his waist, eyes unfocused as he reaches toward something far older than humanity, Senku's fear as he walks out onto the beach and sees jo, hits with a force that startles even Byakuya. It rolls outward through the world in one sharp wave, raw enough to make the hairs on the back of his neck stand up despite no longer having a body. For all Senku insists on logic, on anything besides sentimentality, on never wasting time saying things that don't need saying, there's nothing logical about the panic that floods him when Gen doesn’t immediately respond to his call.
It takes a while for Senku to catch up to his own love.
What can Byakuya say? His son's smart, but he has his blind spots.
All Byakuya ever wanted was for Senku to have people. Support. Friendship. Love, if he wanted it. Someone willing to argue with him when he was being difficult, someone who'd remind him to eat when he'd been working for twelve hours straight, someone who understood that underneath all the confidence was a person who needed other people as much as anyone else.
And somehow that's exactly what Gen becomes. He questions plans, brainstorms solutions, catches problems Senku overlooked because he was focused on the science instead of the human element. He notices when Senku's exhausted before Senku does. He brings him food when he forgets to eat, makes him laugh when the pressure of saving humanity starts becoming too much. He keeps Senku human, and helps him reach for the stars.
It's everything a father could want for his son.
It remains endlessly hilarious that it's Asagiri Gen. Byakuya hopes that once Senku finally realizes he's in love, he'll appreciate the joke too. The kid who used to complain every time Gen's television show came on somehow ends up hopelessly devoted to the magician he'd insisted was full of cheap tricks. Life has always had a sense of humor.
Byakuya can't walk beside Senku anymore. He can't tell him to slow down, can't patch him up after he gets hurt, can't put a reassuring hand on his shoulder when the future feels overwhelming. Those days ended thousands of years ago beside a river on a quiet island. But watching Gen step up, standing beside Senku in all the places where one person shouldn't have to stand alone, eases something he'd been carrying since the moment the petrification beam swept across Earth.
It isn't really letting go. Byakuya doesn't think parents ever completely do.
It reminds him instead of the day Senku learned to walk. There'd barely been a crawling phase; Senku didn’t seem to think he had time to waste with that nonsense. One afternoon his son had simply decided he was done with falling over, pushed himself upright on unsteady legs, and lurched determinedly across their apartment while Byakuya hurried after him with his heart in his throat. Every instinct had been to catch him before he stumbled, but that had never been the point. The point had always been to help him become someone who could keep going on his own.
Now, thousands of years later, Byakuya watches his son doing exactly that. Senku isn't toddling across a cramped apartment anymore. He's walking toward the future, toward the stars, and toward someone who'll walk beside him.
Byakuya couldn't have asked for anything more.