After her divorce, Maya lives alone with her son, Takumi. They have supported each other through daily life, but one day Takumi suddenly stops going to school and locks himself in his room. Worried about him refusing to bathe, Maya suggests, "Let's take a bath together," and Takumi's smile returns during the long-awaited mother-son bath. Relieved, Maya feels at ease—though she has yet to uncover the truth behind his behavior. Around this time, a classmate of Takumi's arrives at Maya's doorstep with a face covered in mud, triggering a new series of events.