Satomi Oka leads his junior high school choir club during his final year, intensely focused on preparing for the last competition before graduation. Though fundamentally sincere, his conversations often carry sharp, biting edges. Puberty's vocal changes strain his ability to hit high notes, jeopardizing choir contributions and solo prospects while fueling deep introspection about his musical identity and future.

His routine shifts unexpectedly when yakuza lieutenant Kyouji Narita, having overheard him sing, requests karaoke coaching. Initially flustered by the demand, Satomi leverages his choir expertise to train Narita, aiming to spare him last place—and an undesirable tattoo penalty—in his gang's annual contest. Their sessions unfold in karaoke rooms, replacing structured rehearsals with one-on-one guidance for an adult gangster.

Beyond teacher-student dynamics, Satomi maintains a cool-headed composure against emotionally volatile peers. Narita drags him into yakuza circles and peculiar encounters with gang affiliates, yet consistently treats him with respect, forging an unconventional mutual understanding. This bond anchors Satomi as he navigates vocal instability and redefines his relationship with music, finding renewed purpose through teaching.

His parents are Yuko and Harumi Oka; choir associates include deputy advisor Morimoto Momo, vice-captain Nakagawa, and member Wada. A sequel during his college freshman year confirms his transition into young adulthood, though his academic path and ongoing musical engagement remain unspecified.