Kenji, Asakura, and Oota are an indifferent trio of school friends, infamous for frequently assaulting fellow delinquents without cause. Weary of the routine brawls that once gave the group a fleeting adrenaline rush, Kenji seeks an alternative outlet by impulsively forming a band. He recruits the rest of his gang, taking up the bass, while Oota handles the guitar and Asakura plays the drums. Although they have no previous experience with musical instruments, their inaugural session greatly surpasses their expectations. Ongaku is a gritty portrayal of three teenage boys, tracing their journey from the moment they uncover the beauty of creating music to their debut live performance, which transforms a mere remedy for boredom into a blazing expression of passion.