Deemo is a lonely individual who lives in solitude, playing the piano in a castle. One day, a girl who has lost her memory falls from the sky. Wanting to help her recover her memories and return to her world, Deemo discovers that a tree kept atop the piano will grow whenever the piano is played.

The fifth musical.

After swearing off music due to an incident at the middle school regional brass band competition, euphonist Kumiko Oumae enters high school hoping for a fresh start. As fate would have it, she ends up being surrounded by people with an interest in the high school brass band. Kumiko finds the motivation she needs to make music once more with the help of her bandmates, some of whom are new like novice tubist Hazuki Katou; veteran contrabassist Sapphire Kawashima; and band vice president and fellow euphonist Asuka Tanaka. Others are old friends, like Kumiko's childhood friend and hornist-turned-trombonist Shuuichi Tsukamoto, and trumpeter and bandmate from middle school, Reina Kousaka. However, in the band itself, chaos reigns supreme. Despite their intention to qualify for the national band competition, as they currently are, just competing in the local festival will be a challenge—unless the new band advisor Noboru Taki does something about it.

Kumiko is now a second year and one of the senior players of the euphonium section. With new underclassmen joining the concert band, Kumiko will have to learn new things in order to deal with awkward and difficult underclassmen. She and third-year trumpeter Tomoe Kabe have been chosen to lead the new underclassmen members. Among the new members to Kumiko's bass section are euphonist Kanade Hisaishi, whose appearances are deceiving; tuba player Mirei Suzuki, who cannot adapt to her new environment; tuba player Satsuki Suzuki, who wants to get along with Mirei; and double bassist Motomu Tsukinaga, who cannot talk about himself. Between the Sunrise Festival, chair placement auditions, and the competition, a number of problems quickly begin to arise.