Four years into her marriage, Ami finds herself growing weary of her relationship with her husband. Spending most days alone, she begins receiving tutoring three times a week from Naomura, a neighboring college prep student. Ami genuinely admires his dedication toward achieving his dreams, and her warmth unknowingly sparks something within him. One day, while preparing for a class reunion and putting on lipstick for the first time in a while, she accidentally collides with Naomura in the apartment hallway—briefly locking lips. From that moment on, Naomura's feelings shift dramatically, and during the quiet afternoons when her husband is away, his desire begins to spiral out of control. An ordinary neighbor's hidden longing starts to pull her into an illicit affair.