In Theory [Senku x Reader]

"What we have once enjoyed we can never lose. All that we love deeply becomes a part of us." – Helen Keller.

The first thing he heard was the ocean.

Waves crashing, slow and steady, lapping against the shore. Seagulls cried overhead, the wind carrying their voices high into the sky.

Taiju blinked down at the golden sand, the brightness was nearly overwhelming under the relentless sun.

Then—laughter.

Not just any laughter he heard. Your laughter.

Taiju blinked—or at least, he thought he did. His body didn't move, but the world shifted around him, fading into an old summer afternoon.

He was a kid again, feet sinking into the warm sand, salt clinging to his skin.

Everything felt distant—voices blurred into an indistinct hum, their owners unclear. He wasn't sure if he was moving, if his head was turning, if he was even speaking. It was all hazy, as though his thoughts lagged a few steps behind reality.

He blinked again, and suddenly, his vision sharpened.

There you were, crouched near the shoreline, fingers sifting through wet sand with focused intent. Senku knelt beside you, a magnifying glass in one hand, inspecting a small marine creature with the same clinical curiosity he afforded everything in the natural world.

Next to him, a glass container sat half-buried in the sand, already filled with various crabs and other organisms—some of which Taiju had never seen before. Not that it mattered. Senku could probably rattle off their taxonomic classifications without breaking a sweat.

Taiju stepped forward, feeling the warmth of a smile on his face—at least, he thought so. Hard to tell. Maybe he'd blame the sun for the lightheadedness.

Right—the beach. They were here because Senku needed to collect samples. Rocks, shells—something for an experiment. Calc—uh, carbon-eat? Carbon-something? He couldn't quite remember, but it had sounded science-y enough that he'd jumped at the chance to help.

His train of thought derailed when you suddenly shot up, holding a small, brilliantly colored shell high above your head. Sunlight glinted off its iridescent surface as you beamed.

"Hah! I found a cooler-looking shell than you!"

Taiju blinked, glancing down at his own hand—when had he even picked up a shell?

He hears himself let out a loud, booming laugh, the kind that came straight from his chest. "Guess you did! Didn't even notice! Can I see it up close?"

Senku barely spared a glance, muttering, "Doesn't matter. We're crushing them up anyway."

You shot him a pointed look—the kind that clearly meant No one cares, Senku. Taiju had gotten good at interpreting those over the years. Without hesitation, you tossed the shell into the growing pile of samples.

Then, as if the exchange hadn't happened, you turned back toward the shoreline, eyes scanning the sand for more finds, the waves lapping at your ankles, dampening the edges of your shorts.

You looked shorter than he remembered. A little more energetic.

It all felt real.

The wind rustling his hair. The salt-heavy air filling his lungs. The warmth of the sun on his skin. And then—

Then, the beach faded.

Darkness crept in, swallowing the light, the scent of the sea, the sound of your voice.