In Theory [Senku x Reader]

0.4 | Call It As It Is

"Perseverance is not a long race; it is many short races one after the other." – Walter Elliot.

'Follow the river downstream, big oaf.'

The message scrawled was simple. Precise. The etching was deep, deliberate—made to last, as if the person who carved it knew exactly what they were doing.

And in Taiju's mind, there was only one person who could have left it.

One person that Taiju knew too well.

Senku.

It had to be him. Who else could it be? If anyone had left behind a message like this, something so calculated yet deceptively simple, it was Senku.

Taiju clenched his fists. His heart pounded, not from exertion but from certainty.

He had to find him. He had to find Senku.

Taiju turned his head slightly, taking in the world around him—the whisper of the wind in his ears, the rustling leaves, the warmth of the sun against his back. And Yuzuriha.

His gaze softened as he looked at her stone form one last time. He burned the image into his mind, locking away the weight of his promise until the day he will have fulfilled it.

Then, without another moment of hesitation—

He ran.

Downstream. His legs carried him forward, faster, the sound of the river's steady current guiding him. Water splashed gently over rocks, a constant murmur against the oppressive silence that accompanied. It was different now. He had direction. He had hope. He had promises that he had to fulfill.

Taiju ran.

Ran as fast as he possibly could.

He needed to know, to see for himself. Of what awaited him down the stream.

Because if that message had been meant for him—if those carved symbols had been etched into the wood with the sole purpose of guiding him—

Then—

Maybe he wasn't—

Taiju's breath hitched, but he didn't stop. His body barreled forward, feet pounding against the dirt floor, kicking up leaves and dust as he ran. His surroundings blurred, a smear of green and brown, trees flashing past his periphery.

"Hah... hah..."

He skidded to a halt, planting his feet hard against the ground, chest heaving as he fought to catch his breath. His head snapped up, scanning his surroundings.

Stillness. Not silence—nature was never truly quiet—but there was no sign of movement, no familiar flash of white hair or a telltale smirk waiting for him in the open. He should be close. Unless—

Did Senku go further downstream?

"Hah..."

He exhaled sharply, dragging a hand down his face. How much farther was he supposed to—?

A rustling.

Taiju barely had time to register the sound before something shifted above him—

And then—

Someone dropped from the trees.

No. Not dropped—hung, suspended effortlessly from a sturdy branch, upside-down, hair swaying with the motion. A grin, wide and teasing, spread across their face.

"You?!"

Your laughter rang through the quiet, bright and unbothered. "Took you long enough."

Taiju's jaw nearly hit the forest floor at the sound of your voice, not a day different than he remembered. "You're alive too?!"