Chapter Text
The lecture hall was filled with excited whispers when Senku took his seat in the back. Pages rustled. Pens tapped. Someone up front was nervously chewing at their pen cap. It was the usual tension before an exam, one part caffeine and one part pure regret.
He set his materials down with confident calm, eyes scanning the room out of habit more than interest. A girl across the aisle gasped softly and held out her arm to her friend. A new message had appeared there, curling across her skin like ivy vines.
Senku didn’t even need to see what it said. Probably some sugary encouragement from her soulmate. Good luck, sweetheart. You’ve got this. Some dumb variation of emotional reinforcement that had zero effect on exam performance but everything to do with oxytocin levels.
Soulmates. The universe’s favorite prank.
The phenomenon was simple. At some point, usually during the late teenage years, a person would find that writing on their skin could transmit messages directly to their soulmate. Same spot, same handwriting. A private line to someone you hadn’t even met yet.
People romanticized it. Idolized it even. Built their lives around it.
Senku found it just inefficient.
He stared down at his own blank forearm. No ink. No messages.
He kept it that way.
Some of his fellow students wore their latest soulmate messages like accessories, proudly displayed with rolled-up sleeves and ink still drying. A few were even writing back and forth right before the exam started. Real smart, distracting themselves from chemistry with heart emojis.
Senku pulled out his pen.
It wasn’t to write anything sentimental.
The exam started. He finished early. Of course he did.
★☆★
The bell finally rang, signaling the end of the exam. The shuffle of papers and the scraping of chairs was immediate. Most of the students sighed with relief and some were groaning at the questions they knew they got wrong.
"Senkuu!"
The voice belonged to Taiju Oki, loud and warm as always. Senku didn’t need to look up to know his childhood friend was barreling toward him like a human freight train.
"Are you done already?!" Taiju asked, panting slightly.
Senku gave him a half-smile. "Thirty minutes ago, actually. You made it look like it was a final boss fight."
Taiju laughed, rubbing his neck. "Figures. I saw your notebook, dude. I think it actually gave me a headache. You had diagrams inside diagrams!"
From behind Taiju, Yuzuriha appeared, her long brown hair swaying softly with each step. She greeted Senku with a bright smile and held up a bento box. "Want to have lunch with us? I made extras!"
Senku blinked. "You made it for him, not me, Yuzu. I'm not going to play third wheel while you two fawn over each other."
"Oh come on, don’t be dramatic." Yuzuriha replied, rolling her eyes. "You're always welcome. Besides, it wouldn’t kill you to spend time with people outside of your lab equipment some more. People who aren’t... test tubes.”
That earned her a half-smirk. “Test tubes don’t expect emotional intimacy. They’re perfect.”
Senku pretended to consider it for a moment. Then sighed. "Fine. But if you start feeding him by hand again, I'm leaving."
★☆★
They found a quiet spot under one of the huge trees on campus. It was spring and the petals of the nearby cherry blossoms drifted soft like rain. Taiju unpacked the bento like it was some kind of treasure. Yuzuriha leaned into his side, laughing when he proudly held up an egg roll like it was a rare gemstone.
Senku sat across from them, biting into a convenience store sandwich like it had offended him.
After a moment of small talk, Yuzuriha glanced at Senku, her look thoughtful. “You know...” she said while resting her chin in her hand “I always wondered if Taiju and I would’ve ended up together even without the whole soulmate thing.”
Taiju blinked. “Wait, we did end up together before the soulmate stuff.”
Yuzuriha bumped her shoulder against Taiju’s. “Yeah but we didn’t need skin-writing to know we already belonged together.”
Senku raised an eyebrow, chewing.
“I already had feelings for him.” Yuzuriha said. “The bond didn’t create that. It just told me I was right. But the feeling itself... it's overwhelming. In a good way. Like, suddenly everything made sense, even if it didn’t before.”
“I thought she was messing with me at first.” Taiju said proudly, pointing at her with his chopsticks. “I was like No way someone this cool wants to talk to me. But we just clicked, y’know?”
“You also dropped your entire lunch tray the first time you talked to me.”
“Out of respect.” Taiju insisted.
Senku snorted.
Yuzuriha smiled, eyes distant now. “When the messages started showing up on our skin, we were excited. But it wasn’t... surprising. Not really. It just confirmed what we already felt. Like the universe was late to a conclusion we had already reached.”
Taiju leaned forward, eager. “It was like getting a message that said Nice job, you found them all by yourself!”
Yuzuriha chuckled. “Exactly. It wasn’t the start of something. It was just proof that we weren’t crazy.”
Senku tilted his head. “So the soulmate system was just... a bureaucratic formality?”
Taiju pointed at him with a rice ball. “Yeah, you get it!”
Yuzuriha’s smile faded a little. She looked at Senku again, more carefully this time. “That’s why I think about it, sometimes. How we might’ve missed each other if we hadn’t been open to the idea of something real, even before the writing. But we gave it a chance, even without proof.”
There was a pause.
Then, gently:
“Do you still get messages?”
The question felt like a pinprick. Sharp and unexpected. Senku froze mid-bite. He chewed slowly, deliberately, before answering.
"Sometimes. Not recently."
"Do you ever answer them?"
"No."
Taiju frowned. "Why not? Don’t you want to meet them?”
Senku shrugged. "Because it's a stupid system."
Taiju blinked. "Stupid?"
"Yes. Unpredictable. Pseudo-romanticized folklore. A psychological misfire wrapped in a social tradition. People just want to believe it means more than it does."
"...Huh?"
Yuzuriha leaned forward now. She was more concerned than confused. "Senku. I get that you love logic and science, but this isn't just some fairy tale. This connection... it's real."
"I never said it wasn't real. I said I don't care."
“I just don’t get it.” Taiju said. “It’s not like the universe forces you to be with them. It just gives you a chance to meet the one person who fits you best. It’s not destiny. It’s... uh... like a soulmate GPS!”
“That’s just a fancy way of saying magical matchmaking.”, Senku answered.
"But what if your soulmate is someone who just gets you? Like truly understands you. Isn’t that worth exploring? Yuzuriha pouted.
Senku looked at her, eyes sharp. "Tze. You know what humanity knows more about? The moon. Our galaxy. Quantum particles. You can map the molecular composition of a distant planet more easily than you can explain why the soulmate bond works the way it does. It’s completely under-researched. People just accept it because it's romantic. Because it feels magical. But we have no rigorous data, no reproducible experiments. Just anecdotes." Senku snapped, a little sharper than he meant to. "We understand nuclear fusion better than the mechanics of this glorified pen-pal system."
Yuzuriha looked hurt, but still didn’t back down. "Just because we can’t explain it doesn’t mean it’s not meaningful."
Senku rubbed at his temple. "Yuzu, I’m not saying it isn’t meaningful to you. I’m saying I don’t trust anything that demands belief without evidence."
Taiju looked hurt. "But it worked for us, Senku."
"Good for you." Senku replied, his voice flat. "But I'm not you. "
He didn’t really mean for it to sound so mean, but the words still landed with a weight neither of them quite knew what to do with. Senku looked away, eyes locked on the half-eaten sandwich in his lap, as if hoping it might spare him from the conversation. The spring breeze ruffled his hair, but he didn’t move.
“I’ve already read studies." Senku eventually murmured, half to himself. "And you know what the scientific consensus is on soulmates? There isn’t one. Nothing but speculation."
Taiju gave him a look. "So?"
Senku sighed. He leaned his head back, staring up at the faint blur of clouds drifting past the stars. Cherry blossoms rustled somewhere nearby. For a while, he didn’t speak. When he finally did, his voice came quieter.
"So maybe I’m just not built to chase phantoms. If the science can’t catch up, I don’t see the point in running after shadows."
There was a pause. Not hostile, but weighty. Yuzuriha’s expression had softened now, more curious than critical. Taiju’s chopsticks had stilled in his hand.
"I’m not exactly starved for company,” Senku added. He waved a vague hand toward them. “I’ve got you two, Chrome’s constant noise, and a father who checks in like clockwork. Throw in my studies, and I barely have time to sleep, let alone emotionally unravel for someone I’ve never met."
★☆★
After lunch, Senku returned to the chemistry lab. The familiar smell of solvents and metal calmed something twitchy in his chest. Science didn’t ask you to believe. It gave you proof. And variables. And clean, predictable outcomes.
The door creaked behind him. Chrome burst in, practically vibrating with energy.
"Heyyy Senku, are you working on the carbon compound model again?" he asked, already dropping his bag by the counter.
"Trying to." Senku muttered. "Until I was interrupted by a walking ball of romantic energy."
Chrome grinned like he couldn’t help it. “I’m in looove, man. Real love. I finally met her! My soulmate. Ruri~.”
Senku raised a brow. “Let me guess. It all started when text magically appeared on your arm one night and instead of questioning the psychological implications, you melted into it just like a poorly constructed marshmallow?”
Chrome laughed. “No! Well... kind of? But it wasn’t just that. We started writing. Just dumb stuff at first. ‘Hi’ and ‘What’s your favorite food?’ and stuff. But then... I don’t knooow, Senku. I felt like I was talking to someone I already knew. It’s hard to explain.”
Senku didn’t respond. He adjusted something on the workbench.
Chrome leaned in, watching him closely now. “She asked me a question no one has ever asked me before. About this weird mineral I collected a year ago. Not ‘what is it’ or something... but why I kept it. Why it mattered to me. Who asks things like that?”
Senku stayed silent.
Chrome’s voice lowered, thoughtful now. “It’s not just the writing. It’s like she’s wired the same way. She thinks in these weird loops like I do. It’s like... I finally met someone who doesn’t just tolerate how I am. She matches it.”
Senku flipped the switch and the burner flared to life with a steady blue flame.
“You don’t believe in it, hm?” Chrome said, not accusing. Just observing.
“I think you’re just seeing what you want to see. That’s not logic. It’s wishful thinking.” Senku said calmly. “And that you’re chemically compromised by affection.”
“You could just say happy.”
Senku didn’t look up. “I could. But then I wouldn’t be me.”
Chrome nudged his arm with a grin. “Talk all you want now. You can’t logic your way out of it once it starts. The bond doesn’t care about theories.”
Chrome leaned in, his voice still cheerful.
“Mock it all you want. Until the first hi crawls across your arm.”
Senku’s face stayed unreadable, but his grip on the glass rod tightened just slightly.
He really hoped Chrome wouldn’t notice. He hadn’t told Chrome.
Taiju and Yuzuriha knew. But Chrome...
Chrome was too full of belief. He’d look at Senku like he was broken for not answering. For not even trying.
And what was Senku supposed to say? That the marks started seven months ago and he treated them like spam mail? That he’d read them, then scrubbed them off like they meant nothing?
That maybe they meant more than he wanted to admit?
No. He couldn’t say that. Not yet.
★☆★
Those conversations stuck in Senku's mind, impossible to keep out. He spent the rest of the day trying to focus on his experiments, but his mind kept drifting away.
It was starting to feel like every conversation was about soulmates in one way or another.
Taiju and Yuzuriha were sweet, sure, but annoyingly so. And Chrome... he used to geek out over volcanic rock. Now he geeked out over Ruri.
Senku couldn’t even blame them. The connection sounded real. Which somehow made it worse.
Why now?
Why them?
Why was everyone suddenly speaking in heart metaphors and soulmate logic?
It made him feel like he was watching a party from the outside of a soundproof window.
His room was silent. The only light came from his desk lamp, lighting scattered papers and open textbooks. Beakers sat quietly on a shelf nearby. Everything in its place. Everything ordered. Predictable.
But his thoughts weren’t.
He glanced at his arm.
Blank.
But for a moment, he remembered.
It was seven month ago when it happened the first time. A little scrawl on the edge of his forearm.
hello?
At first, he thought it was just a trick of the light. But then came the feeling,
a strange, tingling warmth just beneath the skin. Like static and heat and something else entirely. Something unfamiliar. Intimate. Uninvited.
He felt too much at the same time.
Curious.
Anxious.
Thrown off balance in a way he couldn’t quantify.
Then scrubbed it off without answering.
It happened again the next week.
are you there?
No reply.
Eventually, the messages stopped.
He told himself it was good like this. It didn’t matter. He wasn't interested in meeting new people. They’d find someone else. It wasn’t that big of a deal.
Instead it was.
He sat on the floor, leaning back against his bed frame, legs stretched out in front of him. A pen in one hand. His phone in the other.
He scrolled through the message from Chrome again.
Eventually Senku let the phone fall onto his chest. He stared at the ceiling again.
His mind spiraled.
Chrome’s words still lingered on the screen.
Senku had scoffed when he first read it.
But Chrome hadn’t backed down.
Senku had stared at that message longer than he wanted to.
“Curiosity isn’t the same as stupidity.” he muttered under his breath. “Touching an open flame is educational too. Once.”
Still, he didn’t put the phone down.
He was curious. Damn it!
Not about their face. Not about their life. But... their mind. Their voice in the dark. The way they think. The things they believe.
If there was someone out there who thought in a way that completed his thoughts, who challenged him, inspired him... wasn’t that worth investigating?
But the risk...
What if it ruined everything?
What if it turned into expectations?
What if he liked them too much?
What if the idea of them was better than the reality?
He sat up sharply.
But also... what if Chrome was right? What if there was someone out there who just thought like him? Accepted him, understood him in a way no one else could?
Wouldn’t that be worth knowing?
Even if it wasn’t about love. Even if it was just for the intellectual curiosity.
Senku pulled out a pen.
His hand hovered over his forearm.
He hesitated. This was a bad idea. He knew it.
Then, carefully, in small neat letters, he wrote:
Hey. Here are the rules.
I don’t want to know your name.
I don’t want to know anything related to your identity.
But I want to know you.
This is my number: [xxx-xxx-xxxx].
Text me.
Stick to the rules or the conversation is over.
He stared at the message on his skin for a long moment after finishing the last word.
His fingers went still. It was out there now. Whatever happened, happened.
His heart, steady just minutes ago, now beat a little too hard in his chest.
It wasn’t panic. Not exactly. But his body had definitely noticed what he’d done before his mind caught up.
He forced himself to move, walking to the sink like none of this mattered.
He washed the ink away. A variable sent into the unknown.
Then he sat down again.
Picked up a textbook.
Tried to read the same paragraph again and again.
3700 seconds passed, not that Senku was counting, until his phone buzzed.
His pulse spiked.
A new number.
Senku’s stomach flipped.
A strange weight pressed into his chest, full and sudden. Familiar and foreign at once.
He hadn’t realized how long he’d been holding his breath.
Or how fast his heart was beating.
Or how many thoughts were crowding his mind, none of them useful.
He hadn't expected it to feel like this.
He hadn’t expected to feel anything at all.