Chapter Text
Snow fell in a lazy hush, dusting the Kingdom of Science in a fine layer of white. It clung to the rooftops of makeshift buildings and coated the branches of leafless trees, each flake melting on impact with any leftover warmth from the firepit. Inside the workshop was anything but quiet.
It was filled with the eager chatter of Suika and another child, both arguing over the difference between boiling and evaporation, hands flying wildly as they each tried to out-explain the other. Their voices echoed through the wooden structure, bouncing off shelves stacked with glass jars and makeshift lab tools.
Senku stood in front of the blackboard, chalk in hand, coat open despite the temperature. He barely noticed the cold anymore; his brain was too used to overriding discomfort in favour of progress. But today, the override felt more like a glitch than a choice. “—And that, children, is how you separate salt from seawater.”
His voice was steady, even smug, the same tone he always used when declaring victory over the laws of nature. But something in his body lagged, just slightly out of sync with his brain. His hands trembled faintly when he turned back to the table, fingers less precise than usual. The chalk rolled unevenly between them, betraying the subtle fatigue he hadn’t yet acknowledged.
He blamed it on the cold.
“Senku, your face are all red..” Suika had said, eyes wide through her watermelon helmet. “Are you getting sick?” She asked softly, coming closer to examine him. If he was sick she knew to report it to an adult like Gen since Senku was notorious for ignoring being sick in favour of working.
“Absolutely not. Science never sleeps, and it definitely doesn’t catch the flu,” Senku muttered, waving her off with a dismissive flick of his wrist. The words came automatically, easy to say and easier to believe when no one questioned them. But the truth was, he felt off, and not in the usual ‘I-haven’t-slept-in-three-days kind of way’.
He’d tracked the cycles. Marked them down on paper. Gen had even double-checked for him last week, hovering with that infuriatingly smug concern of his. The timing wasn’t right. It shouldn’t be hitting yet. But there was a pull in his chest, low and tight. A soft hum beneath his ribs, like something ancient and territorial curling up and hissing at the edges of his rationality.
It wasn’t desire— no he would’ve recognized that— but it was familiar in a different, heavier way. Something protective. Something wrong in a way that made his skin itch.
He glanced at the kids again. One was scribbling calculations in the snow-dusted dirt floor, another nodding along with Suika's explanation while bouncing on their heels. Another sat half-asleep near the fire, chin tucked to their chest, oblivious to the quiet war Senku was fighting in his own bloodstream.
And something inside Senku shifted, just slightly, but enough to make him stand straighter, more alert. Not the heat, exactly. Not desire. Just… this bone-deep need to keep them close, keep them warm, keep them safe. His instincts had always been a nuisance, something to suppress, override, deny. But in winter? In the quiet? Surrounded by young, vulnerable lives?
They were deafening.
Senku’s gaze lingered on Suika, who had paused mid-sentence, her little head tilted as if trying to solve an equation she couldn’t quite see. Her helmet was dusted with snow, and the way it contrasted with the bright curiosity in her eyes made something stir uncomfortably in his chest. She looked so innocent as she thought.
He could feel the heat pulse beneath his ribs again, subtle but insistent, like a tiny engine revving in the wrong part of his body. Logic dictated that this was inconvenient, irrational, distracting. Yet the pull toward the children— the urge to check their coats, fluff their bedding, make sure they weren’t too cold from the chilly winter air— was impossible to ignore.
Senku moved deliberately to the fire, each step measured so as not to alarm the half-asleep child curled near its warmth. “Here,” he murmured, placing a small bundle of extra wool over the child’s shoulders. His fingers brushed the fabric and lingered a fraction too long, just enough to realize his chest was still tight, uneasy. Protectiveness surged, an instinct older than any science he’d mastered.
It made his vision sharpen, heightening every detail, the child’s shallow breathing, the faint shiver of their body, the way their hair fell across their forehead. Suika’s small voice cut through his thoughts. “Senku… are you… okay?” There was hesitation in it, a slight tremor that suggested she sensed something was different. Not ill, not tired but just… off.
“Yes, yes,” He said quickly, brushing imaginary dust from his coat. “Merely… adjusting to the cold. A scientist must acclimate to all environments, after all.” His words were steady, precise, carefully measured, but they rang hollow even to his own ears. He gently dusted the faint show off of her head and slowly adjusted her coat. It was subconscious.
Turning back to the blackboard, he tried to focus on the lesson, but the numbers and diagrams blurred. His mind was no longer calculating solutions or predicting outcomes.. no. It was cataloging the smallest vulnerabilities around him: a child rubbing their eyes, another tugging at a mitten that didn’t quite fit, the uneven flicker of the fire lighting faces flushed with cold. And with every observation, the tight coil in his chest pulled tauter.
And then he noticed Gen, leaning casually against the doorway, arms crossed, a small smirk tugging at his lips. That smirk… infuriatingly knowing. It was subtle, just a twitch at the corner of Gen’s mouth, but Senku felt like it was aimed straight at his chest, poking at the protective, frantic instinct he couldn’t fully control. Gen soon turned to go help Kaseki who was mere seconds from dragging him away by his coat hood.
Senku froze for just a moment, his rational brain screaming at him to act normal, to suppress the primal tug of his instincts. Do not show weakness. Heat is inconvenient, ignore it. But the instinct wouldn’t be ignored. The children needed him. And, inexplicably, he realized that he, too, needed someone to notice, to acknowledge the tension that had nothing to do with science or reason.
He cleared his throat and turned back to the board. “Now, class—” The words faltered halfway, his voice catching slightly as his body hummed with that bone-deep, almost prehistoric need. It wasn’t desire, not in the way anyone expected. It was vigilance, and it was protective, and it made him sharper, more aware, more tense. He hated it.
A small sneeze from one of the children broke the fragile calm, and Senku moved without thinking, kneeling and wrapping a spare scarf around the child’s neck. The motion was automatic.. instinctual. Senku’s chest tightened further, a coil of tension that was part frustration, part exhaustion, part something he didn’t even have a word for.
He moved from child to child, adjusting blankets, tugging gloves back into place, making sure the smaller ones were safely tucked in near the warmth of the fire. His hands shook slightly, but only in ways that wouldn’t interfere with the delicate tasks. Each check, each adjustment, made the humming inside him grow, spread outward like a quiet alarm signalling vigilance.
By the time he returned to the blackboard, chalk in hand again, his hands were steadier, but his chest still thrummed with the heat, a need. The need to protect, to shelter, to make sure everyone under his watch was safe. It was exhausting and exhilarating at the same time, like standing at the edge of a cliff and feeling the wind both push and pull at you.
And slowly, almost reluctantly, he realized he wasn’t embarrassed. The feeling wasn’t shameful. It was primal and uncontrollable, yes, but it was also a strange comfort. Because the children, oblivious to the internal storm, were safe. And for the first time in weeks, maybe months, the tension in Senku’s chest eased just a fraction. It didn’t vanish— he could feel it humming low, constant, insistent— but it was no longer unbearable.
The lesson continued, Suika babbling numbers and incorrect scientific terms, the other children scribbling in the dirt and snow, the fire crackling. And through it all, Senku remained vigilant, alert and protective. His instincts were running high, his mind racing, but all tethered to something real, something grounding. Soon his class ended and he was quick to get each child to their respective parent before looking over at Suika.
“You ready to go home, little melon?” He asked, voice much softer than usual. ‘Little melon’ was something Gen would use to reference the child, Senku didn’t know why he used it but Suika didn’t seem to notice or mind. She only nodded as she grabbed her little book and came to his side.
“Mhm.. Senku? Can we have fish ramen tonight?” Suika asked softly and Senku just nodded. The words didn’t really click as they usually would, he was more focused on making sure she avoided the big piles of snow and the ice on their way back to the observatory. He grabbed her arm and tugged her away from a big puddle of black ice.
“Careful..” He hissed, eyes tracing her to make sure she wasn’t harmed before he gently let go of her arm. “Sorry.. just, watch where you’re walking? I’d hate for you to slip on some ice.. it dangerous you know..” he then started talking about the dangers of ice before he got to the observatory. He glared at the ladder, he realized it too was dangerous since ice can gather on it.
He’d need to bring that up with Gen later. He lifted Suika up and stayed back to catch her if needed, letting out a sigh of relief as he watched her get in. He followed in before sighing in relief that she’d gotten in safe.
Suika shuffled off to the corner, kicking off her boots ant the door and humming some tuneless little song. Her watermelon helmet clinked softly as she set it down beside her bedroll, and the faint sound of crackling embers from the small metal stove filled the observatory. It was warmer here.. albeit not by much, but enough to thaw the sting from Senku’s hands.
He flexed his fingers absently, watching the faint tremor that still refused to leave. It wasn’t the cold anymore. He knew that. The data didn’t match. The tightness in his chest had changed, less like shivering, more like static, crawling under his skin. It was stupidly unscientific to call it a feeling, but that was the closest word he had.
Suika peeked up from her blanket, blinking sleepily. “You’re not gonna nap again?” She asked, because for the past week Senku had been taking little naps with her ever since she started getting nightmares. He would’ve today but he had some work to do and sadly couldn’t postpone it again.
Senku smiled faintly, crouching to poke the stove with a stick. “Of course not. The stars aren’t going to chart themselves, and we still need to finish that prototype for the wind turbine before spring.” He said softly. He sat down at his little table and lit a lantern. And grabbed some charcoal to write with.
She frowned, her expression small but sharp in a way that made Senku pause. “You always say that.” She said softly, curling up in the bedroll. He didn’t answer. Because she was right. “Wake me up when snack time?” She asked, mind already switching to another topic as she closed her eyes. The wind howled against the observatory’s windows, rattling the wood frames.
Senku rose, glancing outside, the world blanketed in snow, quiet and still. The same world that had once turned to stone and started over from zero. He exhaled slowly, fogging the glass. It was easy to focus on progress, to bury himself in equations and mechanisms. Easier than admitting that something primitive and irrational had been whispering at the edges of his mind since morning.
He turned when he heard a soft shuffle behind him. Suika had fallen asleep mid-sentence, one small hand clutching her little notebook, her face half-buried in her blanket. The sight struck him with a force he didn’t expect. That hum in his chest flared again— protective, grounding, relentless. He hated the way his instincts flared like this. He’d never believed in succumbing to them.
He moved closer, careful not to wake her as he adjusted her blanket again, tucking it around her shoulders. It was a mechanical motion, something he could justify under the label of thermal efficiency. But his hands lingered a fraction too long. The wind outside roared louder, and instinct made him look toward the door, mainly the weak latch that Kaseki had promised to reinforce for them.
His mind immediately mapped potential points of failure; draft gaps, structural weaknesses, ways cold could creep in. But behind that was something else: a mental tally of everything that could hurt her, or anyone under his protection. It was absurd. He was supposed to build civilizations, not babysit them. “Dammit,” He muttered under his breath, rubbing the back of his neck. “This is what happens when you start getting attached to your test subjects…”
But the words held no bite.
He turned back to his table, picking up his notebook, trying to force his brain back into the familiar rhythm of formulas and theories. His handwriting was sloppier than usual; uneven lines, stray marks. He frowned at it, almost offended. He worked for what felt like minutes before a quiet voice startled him. He looked over before noticing the window, it was much darker out then last time he looked.
“Senku…?” Suika hadn’t opened her eyes, but she’d turned slightly, her words slurred with sleep. “Don’t forget to rest too, ‘kay?” She said softly. He froze. The words shouldn’t have mattered. They were small, obvious, childish. But they landed anyway.. like a single snowflake on overheated skin. It made something in him light up.
“…Yeah,” He said softly, barely audible. “I’ll… try.” He said, listening for anything else, but she didn’t answer; her breathing had already gone steady again. Senku exhaled slowly, turning his gaze back to the darkened window. Snow still fell, steady and unending. He reached up and touched the glass, feeling the faint chill.
He looked back at Suika.
Maybe, he thought, progress didn’t only come from logic. Maybe survival— true, human survival— needed this, too. The warmth. The care. The irrational need to protect. He smirked faintly to himself. “Guess even science can’t outsmart biology forever.” The words echoed softly in the observatory, and for once, Senku didn’t try to calculate them away.
He sat down near the stove, notebook open on his lap, the glow of the coals painting his face in amber light. Outside, the snow kept falling, but inside, the kingdom of science — his kingdom— was safe. For tonight, that was enough. He worked a little longer before pulling out some berries and slipping them into a bowl he left beside Suika before he started making dinner.