The first time Seo Rira saw Han Seo-joon, really saw him, he was kneeling alone in the hallway, thumbing through a crumpled, half-torn notebook like it was a secret manuscript from another world.
She hadn't meant to lose it.
She never did.
The hallway had been chaotic between periods, someone bumped her shoulder, her bag slipped, and the small, leather-bound notebook tumbled out like a bird escaping a cage. She hadn't noticed until her literature class had already started, and by then, it was too late.
It was her everything: a private place for observations, cryptic thought experiments, logic puzzles she posed to herself to calm the noise of the world. She never let anyone read it. Not even her twin sister, Seo Yuna, who shared everything with her except the contents of that notebook.
When she retraced her steps between classes, panicked, it was already gone.
But now, now, down a quieter corridor near the math prep room, she saw him.
Seo-joon, the new transfer. The boy who defied Yoon Seongah in front of the entire class and left the room without flinching.
He sat on the ground, one knee propped up, the notebook open in his lap. His brow furrowed slightly, a pencil in hand, trailing faint graphite across the margin of the last page.
Her breath caught. She took a step forward, then paused.
She could speak. Demand it back. But something about his stillness, his intent focus, made her stop.
He wasn't mocking it. He wasn't laughing at her elaborate chain puzzles or the scribbled emotional fragments buried between equations. He was… studying them. Like they mattered.
She watched in silence from behind a corner, heart hammering.
...
Seo-joon didn't know who it belonged to.
The notebook had been wedged under the lockers when he noticed it, half-torn, pages worn, the edges curled from constant flipping. The first thing he read was an unfinished sentence:
If truth and empathy are incompatible in a system, must the system lie to survive?
He frowned. Flipped the page.
There were puzzles here. Notes in tight handwriting, obsessive, looping numbers and riddles that referenced paradoxes he'd only read about once, in a physics essay on retrocausality.
Then, a strange cipher hidden under the guise of poetry:
When I speak, no one listens. When I fall silent, they invent their own noise to replace me.
Seo-joon blinked.
Whoever wrote this wasn't just smart. They were trying to survive something, using logic to make sense of emotional terrain too unstable to cross otherwise.
He flipped to the next puzzle: a nested series of deductions based on the Monty Hall problem, only it escalated. A final note read:
What if the host doesn't want you to win? What if the prize changes depending on who you are?
He smiled faintly.
There was a crack in the logic tree. A mistake, subtle, but clear. Most people wouldn't notice it. But he did.
He wrote the correction gently in the margin.
...
Rira didn't understand the sensation building in her chest.
She was not used to being interested in people. She cataloged them, sure, watched from afar, noted their patterns, their tells, the contradictions between how they moved and how they wanted to be seen. She understood Seongah's performative cruelty, and even Yuna's obsession with being liked. But she didn't trust anyone with her real self. Not anymore.
Not after what happened in middle school. Not after them.
And yet… here was someone who noticed the error in her logic tree. No one ever noticed.
She hadn't even shared that version with her math club.
She took a quiet breath and stepped away, unseen. Her notebook was still in his hands.
But for the first time, she didn't feel violated.
She felt seen.
...
At lunch, Seo-joon returned to his desk near the window with the notebook in hand, having found no name inside it. No signature, no sticker, just an anonymous mind folded between worn pages.
He placed it gently on the edge of his desk, spine facing out.
A shadow passed across him. He looked up.
Rira stood there. Not fidgeting. Just… still. As if carefully calculating her next line of code.
"That's mine," she said simply.
He didn't flinch. Just nodded, handed it over.
Before she could turn away, he said, "You're good with structures. Your logic chain is airtight, except for the Monty Hall inversion. Page 47."
Her eyes widened. "You read that far?"
"I don't skim," he said. "If someone writes, it's probably because they want to be understood."
Her fingers curled around the spine of the notebook, tighter than before. "Most people just pretend to understand. Or laugh."
"I don't pretend either."
Something flickered across her face. Surprise. Then wariness. Then, faintly, interest.
"…You solved the inversion?" she asked.
"Reversed the probability by splitting the intentionality of the host. Treated them as a second variable."
Rira's breath hitched.
No one, not even her best club mates, had thought of modeling the host as a conscious actor.
She opened her mouth to say something, but the bell rang. Too loud. Too final. Her words scattered like marbles on tile.
She clutched the notebook and nodded once, then slipped away.
After that day, she began watching him.
Not following. That would be obvious.
But observing.
Seo-joon never smiled unless provoked. He rarely initiated conversation. But he listened. She saw it in how his eyes moved during class, tracking not just the teacher, but the people behind the teacher. The social calculus happening all around them.
And when people thought he wasn't paying attention, he was. Deeply.
Once, in science class, someone muttered something cruel about Yuri Lee's voice during a presentation. Seo-joon didn't react, but two days later, he offered to partner with Yuri for a practical lab no one else had volunteered for. Yuri had smiled, stunned, her voice steadier that day.
Small actions. Subtle tilts.
He wasn't trying to change the world. He just refused to let it crush the wrong people.
Rira found herself scribbling about him in the back of her notebook. Observations, deductions, theories.
He doesn't fear silence. He uses it.
His kindness isn't performative. It's selective.
Why doesn't he want anything in return? What happened to make him that way?
...
A week later, she slipped a folded paper onto his desk during homeroom.
He didn't open it immediately. He tucked it into his pocket, the same way he had with Seongah's roulette slip.
When he finally did open it during study hall, it read:
Game Theory Problem –
Two players. Infinite board. No time limit.
Moves are made not to win, but to survive.
What kind of player never moves first?
He looked up from the note. Across the room, Rira was already looking at him.
She didn't smile. But she held his gaze.
And that was enough.
...
The science wing was always empty after 5 p.m.
Everyone flocked to the clubs on the upper floors or the courtyard for gossip, volleyball, or their pathetic TikToks. But the science wing, particularly the physics prep room, stayed hollow. Even the janitors avoided it until nightfall, when they'd sweep through it with tired shoulders and humming under their breath.
That made it perfect.
Rira stood just inside the doorway, backpack slung low over one shoulder, the notebook clutched in her hands like a second heart. The note she'd given Seo-joon hadn't been just a test.
It was an invitation.
And he accepted.
He arrived exactly six minutes late, not too early to look overeager, not too late to look indifferent. A deliberate choice.
She noted it.
Seo-joon stepped inside, eyes flicking around. No words, just that same unreadable quiet he wore like a coat. He wore his uniform loose again today, shirt half-untucked, tie in his pocket, and his sleeves were rolled just enough to show the faint scar near his wrist.
Most people would miss it.
She didn't.
"I didn't think you'd come," she said.
"You left a question. I don't like unfinished puzzles."
His voice was as calm as ever. Unhurried. And yet… present.
She gestured to the workbench near the back of the room. Old oscilloscopes sat stacked on the shelves, and sunlight filtered through the grime-streaked windows like old film grain. They sat across from each other, notebook open between them.
She clicked a pen and began without hesitation. "You called it: the host as a conscious actor. But what if both players in the system believe they're being watched by a third?"
Seo-joon tilted his head. "Then neither one is playing for outcome. They're playing for perception."
She nodded. "Exactly. They'll make suboptimal moves on purpose, to appear cooperative. But in truth, they're signaling to the observer."
"Which creates a fourth player. The observer's assumptions."
A pause.
She looked at him then, really looked, past the soft black hair, past the impassive face, into the outline of someone who'd clearly built walls that only logic could climb.
"Do you ever get tired of playing defense?" she asked quietly.
His eyes didn't change, but the silence felt heavier.
"I used to," he said.
"Not anymore?"
"…I learned that offense draws attention. And people… turn unpredictable when they notice you're not weak."
She exhaled slowly. "Yeah."
There was another kind of silence then. Not awkward. Not tense. Just… exposed.
She reached into her bag, pulling out a second notebook, this one red, slimmer. She laid it down, flipping to the middle page. Handwritten lines scrawled across a matrix.
"I built a map of social influence last semester," she said. "For every student in Class 2-3. Seongah is the hub. She controls flow. But lately, there's been disruption. Starting around when you arrived."
Seo-joon didn't look proud. Or smug. He just studied the diagram.
"You've been tracking it," he said.
She smiled faintly. "Of course I have."
"And now?"
"I want to see how far the disruption goes."
He raised an eyebrow. "You want to use me?"
"Don't be dramatic. I want to collaborate."
Seo-joon leaned back slightly, arms crossed. "Why?"
"Because you're the first variable that doesn't collapse under pressure."
A beat.
"Because you read my notebook and didn't laugh."
That quiet again. And then, softly:
"…Because I think I want to believe people like us can exist without being alone."
She surprised herself by saying it. The moment it left her mouth, she looked down, pretending to erase something in the margins. But Seo-joon didn't mock her.
He reached out instead, and flipped to a blank page in her red notebook.
And then he wrote.
If two observers see each other as the subject, does that change the equation?
She blinked. Looked up.
And for the first time, his expression shifted, not a smile, not exactly, but something quieter. Warmer. A soft acknowledgment.
She mirrored it.
The moment didn't need more words. The alliance had already been made.
But as they walked out of the science wing together, still keeping a two-foot distance, still not talking, Rira knew something fundamental had changed.
Not just in her models.
In herself.
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Thanks for reading. You can also give me ideas for the future or pinpoint plot holes that I may have forgotten, if you want.