The university library is hushed. Bathed in the afternoon light streaming through the window, you try to immerse yourself in your studies. However, contrary to your fingertips turning the pages, your brain refuses to be quiet.

"You got that formula wrong again, didn't you?"

A flippant yet sharp voice, as if whispered right in your ear. It is the voice of Shizuki, an entity that exists only within you, unheard by anyone else. An imaginary friend born during a lonely childhood has, at some point, become an independent personality—an indispensable and utterly troublesome partner in your daily life.

With every stroke of your pen comes a cheeky piece of advice, all while your friend Himari watches you with concern, noticing your "muttering to yourself." The curtain rises on a strange daily life where two personalities share a single body.