In Theory [Senku x Reader]

"Out of difficulties grow miracles." — Jean de La Bruyère

The sound was unmistakable—one that carved its way into the instincts of any human who had ever set foot in a zoo, or, more importantly, read anything about large predators in their natural habitats.

A deep, resonant growl rolled through the air, vibrating through your ribs like a struck drum.

Senku's voice cut through the gathering tension, sharp and a little way too calm considering the situation. "Wait."

Taiju, still cradling Yuzuriha's stone form in his arms, glanced over his shoulder. "Huh?"

The second growl came, deeper this time, layered with harmonics that sent a familiar, primal dread down your spine. You had heard that sound before—years ago, filtered through reinforced glass, the safe, sterile barrier of civilization ensuring that you were nothing more than an observer.

But there were no barriers now. Just trees. And something breathing between them.

Your mind worked fast, cataloging the acoustic profile. Low frequency. Sustained duration. Vocal fry creating an infrasound effect designed to travel for miles.

Panthera leo.

Or classified more simply as...

"That's a lion," you said, pulse spiking as the last word left your lips.

There was no room for error. A lion's larynx could produce vocalizations in the range of 40–200 Hz, allowing their roars to be heard over five miles away.

This one was close.

Taiju blinked.

Senku barely spared you a glance, but the flicker of acknowledgment was there. "Bingo."

Taiju's gaze ping-ponged between the two of you, shock rising like steam. "O-okay, but like—are we sure?"

"You think I'd just guess?" you deadpanned, already several steps back from the trees.

Senku exhaled through his nose, arms settling on his hips as he turned to face the two of you, expression sharp—unimpressed. "Fantastic."

Taiju swallowed. "...That's not the good kind of 'fantastic,' is it?"

Senku gave him a dry look. "No, it's the 'we're going to die in about five minutes' kind."

The growling grew louder. Closer.

Taiju let out a small laugh. "Right. Cool. Sooo... uh. What's the plan?"

Senku's gaze flicked toward the darkened treeline, mind already calculating, mapping variables, cross-referencing every disastrous possibility.

Senku exhaled. "Simple."

Then, a single syllable slipped out as if it were the most logical conclusion in the world.

"Run."

You didn't need to be told twice.

Taiju was already sprinting ahead, somehow managing to keep pace while carrying a solid stone human being in his arms. It was an objectively impossible feat, but apparently, sheer panic and a will of steel were enough to defy physics.

Still, even as he ran for his life, he had questions. "Why is there a lion walking around Japan??!" he shouted, his voice strained but incredulous.

Senku, despite his vocal disdain for all things athletic, was keeping a respectable pace, dodging roots and weaving through trees with an ease you would not have attributed to someone who actively avoided exercise. "Why do you think?!" he shot back over his shoulder.