Haruta and Chika, childhood friends, decide to form a music duo and join their high school's wind ensemble club to pursue their passion for music.
Chika and Haruta encounter their first mystery within the music club involving missing music sheets, which they solve using their keen observation skills.
The music club faces the possibility of being disbanded due to lack of members, but Haruta and Chika recruit new members and save the club.
Haruta, Chika, and the music club participate in the annual wind ensemble competition, delivering a remarkable performance.
The duo investigates and unravels the hidden tensions between rival schools during the competition.
Chika composes a new music arrangement for the upcoming graduation concert, marking her growth as a musician.
The music club performs the graduation concert successfully with Haruta's leadership and Chika's arrangement.
In their final days before graduation, Haruta and Chika reflect on their experiences and friendship through the music club.
