Oumae Kumiko, a girl with absolutely no ambition, decides to change herself now that she has started her high school life. After all, her junior high school life was forgettable as she calmly accepted the "dud-gold" with her brass band club — effectively failing to go beyond the regional selection. She doesn't want anything to do with another brass band club in her new school, let alone with the wind instrument 'Euphonium' that she used to play.
Now that she is in high school, she is pinning her hopes on having a slightly attractive bosom; perhaps even wearing her skirt a bit shorter will bring about the change she seeks.
Kumiko quickly becomes friends with Hazuki and Sapphire from her class. Strangely however, she finds herself checking out the brass band club with her new friends despite having no interest at all. To make matters worse, she identifies one of her brass band classmates from junior high in the clubroom — Kousaka Reina, a girl she had 'an incident' with at the regional brass band club competition. There's absolutely no way she can afford to join the brass band now!