Hibike! Euphonium Series: Rikka Koukou Marching Band e Youkoso

The story focuses on the Rikka High School Marching Band. Azusa Sasaki, Kumiko's friend from the middle school, is the main character of this novel. It is set around the same time as the main series but it is told from Rikka High School's perspective instead of Kitauji's. (Source: Hibike! Euphonium Wiki)