Chapter Text
He’s working on the ship design in their newly built lab when he feels his eyes start to burn. It’s late at night; most everyone went to bed hours ago, but he needs to finish the drawing for the ship design contest Gen set up for tomorrow.
It’ll get everyone to buy in, Gen had said, fluttering his hands like it was obvious. And maybe it was. They had too many people now to just tell them what to do, too many who led with brawn instead of brain. With Tsukasa in his frozen deep sleep and Hyoga locked away, the balance was still fragile, held together by clever words, uneasy truces, and a lot of hard-earned trust. Senku wasn’t exactly keen on figuring out which new power-hungry meathead wanted to challenge him next. So he’d gone along with the contest, even though he thought the whole idea was stupid.
He scrubs at his eyes, smearing graphite and fatigue across his face, and keeps working. The lines of the cabins are too sharp. He redraws them. Again. The burning doesn't fade. In fact, it’s getting worse.
He’s never been a crier. Byakuya always said it was a little eerie, when he was a brat - he’d fall, scrap his knee, and immediately start reciting facts about how the body heals while it was his dad who panicked. But this feeling isn’t quite like what he’s felt the few times he has cried. There’s an odd pressure behind his eyes, a burning feeling across the bridge of his nose. It feels like someone is scraping a butter knife across his cheeks.
He sits up, pressing his hands against his face, trying to breathe. The pain is distracting.
That must be why he misses the soft padding of footsteps. “Senku dear! You need to sleep. Look at you - you’re going to combust at this rate.”
“Go away, mentalist,” he mutters, blinking through the sting. His voice is rough. Even talking feels like effort. The pain is mounting now, settling into his skull like a second pulse.
There’s a pause. Then a shift in tone. “Oh? Is something wrong?”
Cool fingers grip his hands and gently tug them away from his face. Senku lets him. The discomfort of someone touching him is nothing compared to the burning pain across his face. Gen’s touch doesn’t really ever bother him anyway.
He wonders, absently, if he’s having some kind of allergic reaction. Maybe something in the graphite? The paper? A chemical in the ink? His breathing is very measured and controlled.
“Your eyes are all red,” Gen says, frowning - no coy smile, no teasing. It’s more serious than Senku has seen him look in a while. There’s an edge of alarm in his voice. “What’s wrong with you?”
“I’m not sure,” Senku mumbles, squinting up at him. Gen looks paler than usual in the dim lab light, his dark circles deepened by the shadows. He’s still holding onto Senku’s wrists, fingers steady even though his eyes are scanning Senku’s face like he’s a puzzle he can’t solve. “Just started hurting out of nowhere.”
“Your eyes are starting to water,” Gen says.
He reaches up to touch his cheek, half-expecting to find tears. But instead of wetness, something tiny and hard drops into his palm with a delicate plink.
A perfect crystal. Less than the size of his pinky nail, it's shaped like a star - five-pointed and impossibly intricate, clear as snowmelt and colder than ice. It glints in the low lamplight.
They both stare at it.
Gen doesn’t say anything. His breath catches audibly in the silence.
“What the fuck, ” Senku says flatly.
“This wasn’t something that happened to you before the petrification, was it?” Gen asks. He’s let go of one of Senku’s wrists, hand hovering over the glass star like he’s afraid to touch it.
“I barely ever cried,” Senku says. His voice is distant, analytical, like he’s reading data aloud. “Let alone cried glass stars.”
He turns the tiny object over between his fingers, watching it catch the lamplight again and again. It really does feel like glass, cool and flawless. The pain across the bridge of his nose hasn’t gone away, but it’s dulled now, like the edge of it has worn off.
Then another star slips free from his other eye. He feels it fall.
A moment later, a faint tink sounds from the floor as it shatters.
Senku doesn’t flinch at the sound of the star shattering. He just stares at his hand, still holding the first one - whole, glittering like ice beneath a microscope. It refracts the lab light in strange, almost impossible ways. Part of him wants to grab the nearest beaker and start testing its structure, but another part is frozen, still trying to catch up to the fact that it came out of his eye.
Glass. Or something like it.
"That shouldn't be possible," he mutters. "There's no mechanism in the human body to crystallize saline, let alone into geometric forms like this. No temperature drop, no binding agent, no nucleation point -"
He stops talking. Something is coiling within him, slowing his thoughts. Dread is draped across his shoulders like a blanket.
He places the star gently on the table beside him, almost reverently, then wipes at his other eye. His fingers come back dry. No blood, no tears. Just heat.
“…Maybe I’m hallucinating,” he says out loud, voice distant. “Microcracks in my cornea causing light distortion. Or a stress-induced ocular mirage. Sleep deprivation can mimic psychosis.”
Gen doesn’t answer. He’s crouched beside the table now, retrieving the shattered piece from the floor with a carefully folded cloth like he’s handling radioactive material. Senku watches him out of the corner of his eye.
“These feel real to me,” Gen says, putting the cloth on the table in front of him. Glass shards, thin and delicate, glitter like tears.
“The burning is gone, at least,” Senku says, pressing his hand against his cheek. The heat is dissipating, but his skin still feels raw. He’s suddenly exhausted.
Gen doesn’t respond right away. He’s still poking gently at the shards, expression unreadable, mouth drawn in a flat, serious line.
Then, finally: “Time for bed, I think.”
Senku frowns. “But - ”
“No.” Gen snatches the pencil from his fingers in one fluid motion and sets it firmly out of reach. “Your drawing’s fine. And we both know you’ll blow everyone else out of the water even with half a plan and one eye closed.”
Senku opens his mouth, then shuts it again.
“Fine,” he says. “We’ll get through this, then we figure out what these tears are.”
“Of course,” Gen says. He trails his hand along Senku’s shoulder for a moment. Something curls in Senku’s gut, past the haze of confusion and exhaustion, something he can barely even describe.
Gen walks beside him, close enough to touch, not quite guiding but never straying more than a step away. Senku’s swaying slightly as they leave the lab, muscles aching, his head pounding with each step. He’s vaguely aware of how quiet the camp has become, of how distant the stars look tonight. Maybe they've fallen out of the sky and into his eyes, he thinks, and then feels silly.
When they reach the tent they share, Gen pulls back the flap and gestures him in. Senku ducks inside, stumbling slightly, and doesn’t protest when Gen gently sets him down. He watches through half-lidded eyes as Gen rolls out his sleeping mat and arranges the blanket over him with careful, practiced ease.
Senku lies back, arms limp at his sides, the exhaustion hitting harder now that he’s horizontal. His body sinks into the mat like stone. He can still feel warmth where Gen had touched him, on his wrists and along his shoulders. His mind is spinning, but not fast enough to keep him awake.
“Sleep well, Senku,” Gen says from nearby, his voice hushed. Senku hums a response, barely audible.
And then the dark takes him.
—
The next morning, the sky is cloudless and sharp, blue as crushed stone. Gen had brought Ruri by, with the logic that as the priestess of the village, she might have the best idea of what the glass stars are. It's nothing they're familiar with from the modern world.
“I have heard of this,” Ruri says softly, crouched beside the worktable. Her fingers hover just above the broken glass shards, careful not to touch. Gen holds the cloth open in his palms, revealing both the fractured remnants and the single, perfect star. They shimmer in the bright sunlight. “Though there hasn’t been a case in the village in years. It’s not a common disease. More of an old story, really.”
Gen watches her carefully. “But a real one?”
She nods slowly. “As far as we’ve been able to tell. It’s said to be driven by extreme emotions, ones the body can’t contain. The tears turn solid. Crystallize.” She pauses, then adds, “Not always into shapes like this, though. That part is…new.”
Gen’s eyes drop to the star again, impossibly clear and cold in the sunlight. It looks more like a snowflake carved by hand than anything that should come from a human body.
“How odd it is that it’s our dear Senku who developed it then,” Gen says lightly.
Senku doesn’t disagree with Gen’s assessment, actually. It is odd. He’s not sure he’s felt anything unusually strong lately. No breakdowns. No intense surges of fear or grief. He’s been working, planning, building - business as usual.
“Well,” Ruri says gently, “we did just win the war against the Empire of Might. Then Tsukasa was stabbed. And before that, you found out your father was gone. Perhaps it’s just everything catching up to you.”
Senku meets her gaze. Doesn’t flinch. “But I’m fine,” he says, firmly.
Ruri tilts her head. “Are you?”
He opens his mouth. Closes it.
What is he supposed to say? That grief is inefficient? That guilt over Tsukasa is illogical? That he’s already processed all of it? Filed it neatly away under “irrelevant emotional interference” and moved on?
Senku crosses the room and looks down at the star lying in the cloth. It catches the light, casting tiny prisms onto the surface of the table.
“That came out of my eye,” he says. Flat. Scientific. But the words still feel unreal. The little star is too pretty and delicate to have been born from pain, if that’s even where it came from.
“It did,” Gen replies, quiet now. “And I don’t think it’ll be the last time.”
Senku watches the glinting crystal for a moment longer. Then, softly: “I didn’t even feel anything.”
“Some people cry because they’re overwhelmed,” Gen says. “You wait until the pressure turns you into a walking geode.” He spreads his arms with a casual flourish, like he’s unveiling a magic trick. “Ahh, dear Senku is truly one of a kind! Who needs Kaseki to blow glass when your eyes can do it?”
Senku snorts, sort of despite himself. “Don’t tell anyone else about this, for now,” he says. “We’ve got too much on our plates.”
Ruri wrinkles her nose, looking displeased. “You’re the chief, and I am honor-bound to listen,” she says. “But as your friend and ex-wife, let me tell you I think that that’s a terrible idea.”
“If this is tied to feelings, I need the space to parse it out,” Senku says. He doesn’t really think it’s tied to feelings - surely, he’d feel something so strong that the connection was obvious, if that were true. “I can’t do that if everyone’s crowding me.”
People are always putting his feelings in his mouth, he thinks, like they know what is going on in his head. It was frustrating enough in the modern day, when he couldn’t explain his frustration, the full scope of his dream to reach the moon. But now, 3,700 years in the future, beyond the death of his father and in the aftermath of a war, post one near-death experience already, it grates on him.
It’s bad enough that all of humanity depends on him. He doesn’t need their interpretations of his own emotional chemistry layered on top of it.
Gen is watching him, face blank, hands tucked into his sleeves.
“I’m not repressing anything,” Senku mutters, without looking up.
“I didn’t say you were,” Gen replies, tone soft, neutral. But his eyes don’t leave Senku’s face. “Just saying...sometimes the body remembers what the mind can’t catch.”
Senku stiffens.
The table between them is quiet. Light dances across the fractured glass. Ruri looks between the two of them, her expression pinched with concern, but she doesn’t interrupt.
Finally, Gen folds the cloth closed again, tucking the star and shards away like precious evidence. “I’ll keep it secret, for now,” he says. “But I reserve the right to worry excessively in silence.”
Senku rolls his eyes, but there’s no real irritation behind it. He just turns toward the door. “Let’s get this stupid competition over with,” he says, already walking away.
Gen’s brows lift. “My, such passion. One might think you were emotionally compromised,” he teases, trailing after him.
Senku doesn’t dignify that with a response. And Gen, to his credit, doesn’t press. Just walks beside him, close enough to touch.
—
He can’t quite pin down the pattern behind the heat flushing across his face - the slow, building pressure that always comes before more glass tears spill free. They strike late at night, or sometimes in the quiet early hours before dawn. Once, he’d even bailed on lunch early because he could feel the burning rising in his cheeks like a warning flare.
More stars keep coming, and sometimes they scratch at his skin as they fall, sharp edges catching on the tender surface. It’s been obvious enough that Taiju’s started to fret about what’s wrong with him, which only adds to Senku’s irritation.
Gen is usually nearby when the attacks hit. He distracts the others, quietly lures them away so Senku can endure the episode in silence. Then, with gentle precision, he dabs disinfectant onto Senku’s face, his hands cool and steady against the burning heat.
Afterward, Gen collects every little star that survives the fall, carefully placing them in a box that stays hidden deep in their tent, far away from curious eyes. He’s made it clear to anyone who might wonder that messing with their things will be met with consequences - he’s no stranger to curses or clever traps.
The villagers are slowly warming to science, but old superstitions still linger, and some still wonder if magic might be real. The modern-timers know better. They know Gen is vengeful, fiercely protective, and incredibly sneaky. It’s best not to get on his bad side.
Senku hates how vulnerable the glass tears make him feel. Every time one slips free, it’s like a quiet betrayal, a physical sign that something inside him is cracking, even if his mind insists otherwise. He hates being seen as weak, especially now, when everyone looks to him like a pillar, like the unbreakable force keeping humanity’s fragile future alive.
What frustrates him most is the lack of a scientific explanation. Ruri called it a disease, but nothing in their known biology, ancient or modern, can account for the crystallization of tears. There’s no data, no method of testing, no control group. He’s left with folklore and speculation.
Worse still, the so-called cure is rooted in something intangible - emotional healing, catharsis. The kind of shit that appeared in self-help books. Things he can’t quantify, can’t break down into compounds or equations. He can’t experiment his way out of this.
Ryusui, at least, is a useful distraction. Loud, flamboyant, and endlessly theatrical, his arrival has refocused the village’s attention toward commerce, ambition, and indulgence. Bread, banquets, and bravado have bought Senku a little breathing room.
Right now, he’s distracting them all with Yuzuriha’s high-end fashion show. Senku can hear it in the distance: the laughter, the music, the enthusiastic cheers as villagers parade in hand-stitched designs. The clamor of a world trying its best to move forward.
Senku sits alone at the edge of the beach, waves licking at the sand near his boots. The pressure is building again. Heat blooms behind his eyes, spreading down his cheeks. He presses his palms into his face, grinding the heels of his hands into his sockets, trying to force it back down.
The unfinished skeleton of their ship juts into the sky nearby, stark against the horizon, a dream half-built. A reminder of where they’re going, of what he has to hold together.
“Dear Senku?” Gen’s voice comes from behind him.
The surprise breaks his control. Instantly, the pressure spills over. The tears fall with a quiet chime, tiny crystalline tinks against his palms. They burn going down, sharp as glass should be. Some of them cut, slicing thin, stinging trails into his cheeks. He gasps from the shock of it.
Humiliating.
He cups his hands beneath his face, trying to catch them before they shatter in the sand. The stars glitter in his palms like cursed jewels. Look at him - crying like a child, like a weeping maiden in a fairytale. Ridiculous.
Gen pads closer, his shadow long and steady. He kneels in front of Senku and gently lifts his chin, tilting his face toward the moon.
Senku resists for half a second, then lets him.
Moonlight catches Gen’s hair, making it glow silver-blue, like the tears that fall from Senku’s eyes. His expression is unreadably soft, brows furrowed in quiet worry. He examines Senku’s face, his thumb brushing just under one eye with careful pressure.
“We’ll need to clean these off,” Gen murmurs, mostly to himself. “They’re starting to cut deeper.” Senku lets Gen tilt his face, looking at the cuts, the tears still building in his eyes. “What was happening before this round?”
Gen’s been asking that lately, trying to help Senku build up a pattern of what triggers the tears.
“I don’t know,” Senku admits, digging his toes into the sand. He’ll get sand in his shoes, but he needs something to anchor himself from the burning pain. “I was just watching Yuzuriha’s show when I felt it.”
“Mm. And how did that make you feel?”
Senku glares at him. “Like I was observing a successful textile operation with strong village engagement.”
Gen doesn’t flinch. “Try again.”
Senku digs his toes into the sand, letting the grit bite into his soles. He wants to give an answer, but all he has is static. A blur of noise and pressure and something like pride, maybe, and something like loneliness.
“I don’t know,” he says, quiet this time. “It wasn’t bad. It just…started.”
“It’s not a bad thing, to feel things,” Gen says.
“I know,” Senku says tightly. “But that’s not the issue here.”
Gen just looks at him, mouth flat. “Tell me about your dad,” he says abruptly. It’s so out of left field that Senku can’t help feeling surprised.
“Why do you want that?” he asks.
“Indulge me,” Gen says.
“He was…” Senku starts, then stops. He frowns. “He was a terrible singer. Like, impressively bad. He used to try and serenade me while he was making dinner and I’d have to escape the kitchen before my ears bled.”
Gen gives a faint, encouraging hum. He doesn’t interrupt.
“He was a good professor,” Senku goes on. “Which is funny, because he wasn’t great at explaining things to me. I think he struggled with how fast I picked stuff up. Maybe he didn’t always know how to talk to me.” He swallows. “He sold his car to buy me scientific tools,” Senku says, quieter now. “I don’t think I ever thanked him for that.”
The burn comes back suddenly, roaring through his face like a flare. He gasps, hands flying to his cheeks. Glass tears fall again, but this time, they mix with something wetter. Salty. Normal.
Liquid tears, streaking down his face alongside the crystalline ones. The salt stings as it hits the open cuts, and for a moment, all he can do is hold his hands to his face and breathe through the pain.
Gen leans forward just enough to peer at Senku’s face. His hands are gentle as he lifts Senku’s wrists away, just enough to see the mix of wet streaks and crystal trails clinging to his skin.
“…Well now,” Gen murmurs, eyebrows lifting slightly. “That’s new.”
Senku blinks at him, dazed. “What?”
Gen taps lightly at Senku’s cheekbone with a knuckle. “Some of these are liquid. Not glass. Look.” He reaches for the corner of Senku’s eye with the edge of his sleeve and dabs carefully. “They’re warm. Salt water. Ordinary tears.”
Senku frowns, then sniffs hard, already annoyed that his nose is running too. “Fantastic. Now I get both. That’s incredibly efficient.”
“I’d call it progress,” Gen says, voice mild but eyes sharp. “Liquid tears, when they make sense, are far preferable to your usual face-slicing variety.”
Senku is silent for a beat. The burning has eased a little, and the pressure behind his eyes doesn’t feel quite as sharp. He wipes the rest of his face with his sleeve, trying not to wince at the sting, and mutters, “Could be a dilution effect.”
“Come again?”
“The saline in regular tears could be diluting whatever compound is causing crystallization.” Senku starts talking faster, thinking out loud like it’s the only way to stay grounded. “There could be a threshold - a saturation point. If the body is finally producing enough fluid output, maybe it can’t supercool into solid form fast enough.”
Gen raises an eyebrow. “So your big breakthrough is that you cried better?”
Senku scowls at him. “It’s data. Not a cure.”
“Mm. No, but it’s something. And,” Gen adds pointedly, “It happened when you were talking about your dad.”
Senku grimaces. “Correlation isn’t causation.”
“But it is suggestive.” Gen reaches out again, softer this time, brushing a thumb carefully across a healing cut on Senku’s cheek. His fingers are cool and gentle. Senku can hardly stand it; no one has touched him with such care, like he’s fragile, in years. “So is the fact that your body stopped trying to cut your face open the second you said something real.”
Senku doesn’t answer. He stares out over the water instead, jaw clenched.
Gen sighs. “I’m not trying to make this harder,” he says, voice softer now. “We don’t know what these tears are doing to you. What they’ll keep doing, if we ignore it. I just…” he breaks off, then finishes quietly, “I’m worried it’s going to get worse.”
You and me both, Senku thinks.
Gen’s thumb lingers a second longer on Senku’s cheek before he lets his hand drop. The waves murmur in the distance, soft and steady, and for a moment neither of them speaks.
“Senku?” a voice calls in the distance. “Gen?”
They both flinch.
It’s Kohaku, her voice closer than it should be. Gen’s head snaps toward the path through the trees. Senku quickly swipes at his eyes, instinct kicking in hard. He scoops up the glass fragments from his lap and shoves them into his coat pocket, careless of the sting.
“Here!” Gen calls, rising to his feet and positioning himself between Senku and the approaching noise.
She crashes through the underbrush, sticks stuck in her wild hair. “There you are!” She pauses, clearly noticing Senku’s red eyes, the tear tracks across her cheeks. Her eyes narrow. “Is everything alright?” She’s protective of him, Senku knows.
“Oh, yes,” Gen says breezily. “Just chatting about workplans. What’s up?”
“Yuzuriha was looking for you, Gen,” Kohaku says slowly.
“Ah, thank you. I did need a break from the sound, but all better now!” He stands up, dusts the sand off his coat. “Thanks for the chat, Senku,” he says, and disappears into the trees.
Kohaku lingers. “You’re really okay?”
Senku doesn’t turn. “I’m functional.”
“That’s not what I asked.”
After a pause, he says, “Go help with the show, Kohaku.”
She doesn’t argue. But she doesn’t move either, not for a long few seconds. Then the sand shifts as she steps back, and finally her footsteps retreat toward the village.
Then he exhales through gritted teeth, pulls the jagged glass fragments from his pocket, and holds them in his palm. The moonlight catches them, turning them silver and sharp, tiny traitorous proofs of something he still doesn’t know how to name.