Hibike! Euphonium begins when Kumiko Oumae, a girl who was in the brass band club in junior high school, visits her high school's brass band club as a first year. Kumiko's classmates Hazuki and Sapphire decide to join the club, but Kumiko sees her old classmate Reina there and hesitates. She remembers an incident she had with Reina at a brass band club contest in junior high school.
