Ototama ~Boku-tachi Girls Band Desu~

A childhood promise, ten years and a growth spurt later, turns out to still be on the table. The protagonist transfers back to his old hometown school expecting nostalgia and instead gets blindsided by the once-familiar boy who's now unrecognizable and very much still remembering what they swore to each other as kids.

That reunion kicks off a band, formed with three other boys and aimed squarely at the school's cultural festival stage. Rehearsals, practice sessions, and the daily grind of getting a group of teenage boys to actually play music together end up doing less for the plot than the time they spend alone together, where the bonds the story keeps talking about start meaning something else entirely.

Play follows the four of them through school life and band practice toward that festival performance, with the relationships between the boys developing along the way rather than being decided upfront. It's a voiced visual novel told through 2D scenes, so there's reading and choosing, not much else, and the focus stays on the cast rather than on staging elaborate spectacle.