Prologue: The First Promise

August, 2024. The air in the Midori Primary School playground was thick and hot, humming with the noise of cicadas.

Karuizawa Rin (12), sitting alone on a low stone wall, meticulously arranging the contents of her pencil case. She preferred the quiet logic of her world to the chaotic social dynamics of the fifth-grade class. That was, until a shadow fell over her.

Hashimura Yuta (12), all elbows and unruly dark hair, stood before her, looking sheepish. He wasn't the top of the class, but he was certainly the loudest.

HASHIMURA YUTA

Hey, Karuizawa-san, right? You dropped this near the water fountain.

(He held out a small, metallic silver Logic Puzzle keychain—a complicated geometric shape that Rin treasured.)

KARUIZAWA RIN

(Reaching out quickly, her face stoic) Thank you.

HASHIMURA YUTA

It's a weird one. My dad has a couple of those in his office. Says they’re for “brain calisthenics.”

(Rin, usually silent, felt a small spark of connection. She explained its mechanics, and Yuta, instead of getting bored, listened intently, his head cocked.)

KARUIZAWA RIN

It’s complex. You have to anticipate three moves ahead just to solve the first permutation.

HASHIMURA YUTA

(Grinning, the kind of open, silly grin that melted through her defenses) Huh. Sounds like you're the one who needs the brain calisthenics, Rin. You’re already too smart!

(Rin laughed—a genuine, surprised sound she rarely made. Over the next few weeks, Yuta kept finding reasons to talk to her. He’d point out absurd things the teachers said, whisper bad jokes during recess, and once, he spent twenty minutes trying (and failing) to solve her puzzle. Rin saw the funny, genuine, and kind side of Yuta—a side the rest of the class didn't get to see.)

One late afternoon in September, they were walking home near the park. The setting sun bathed the street in a warm orange glow.

HASHIMURA YUTA

Hey, Rin.

KARUIZAWA RIN

(Looking up at him, her heart already beating faster) What is it?

HASHIMURA YUTA

(He stopped, looking unusually serious. He fidgeted with the strap of his backpack, taking a nervous breath.) I like you. I like hanging out with you more than anyone else. You’re smart, and you laugh when I’m being stupid.

(He didn't make a big deal of it; it was quiet, honest, and felt like the most important truth in the world.)

HASHIMURA YUTA

I know you like logic. So, let’s be friends. More than friends. Let’s be partners. Can we be partners, Rin?

(Rin’s heart felt light, buoyant. This was the first time anyone had valued her for her whole self. She didn't need logic to figure out this answer.)

KARUIZAWA RIN

(Smiling brightly) Yes, Yuta. We can be partners.

(They linked pinkies, sealing the promise. This was the beginning of their bond—a pure, fragile connection waiting to be shattered.)