Kenji, Asakura, and Oota have a reputation for their apathy towards academics and tendency to engage in physical altercations with fellow toughs. Tired of their monotonous cycle of directionless aggression, Kenji proposes they form a musical group. Despite having no previous knowledge of music, they take up instruments and remarkably thrive during their initial rehearsal. Ongaku documents the expedition of three youths as they uncover the thrill of producing melodies, culminating in an impactful concert fueled by their recent infatuation.