Kakeru Kurosawa is an antisocial junior high school student. He rarely associates with his classmates, and he looks down on them. But this behavior is topped off by a certain bad habit, his closely guarded secret: every day after school, he sneaks in to the rarely used girls' toilet on the 3rd floor and masturbates in a stall.
Kakeru's shadowy routine remains undisturbed until one day, when a diminutive girl from his class, Aya Kitahara, almost discovers him. Their meeting begins a coming-of-age story dealing with blackmail, bullying, revenge, heartbreak and ultimately, redemption.