Sotaro Shiomi, the ace pitcher of his high school baseball team, is forced to quit the sport due to an injury. Losing his purpose, he heads to the school rooftop with the intention of jumping, but is stopped by a classmate, Lucy Komatsubara, who casually invites him to join the brass band. Intrigued by her simple offer, he accepts and enters a world far more chaotic than he expected. The brass band is in a state of constant turmoil: the president, Hidaka, is a hot-blooded gal type who wants the club to aim high; the vice president, Kurami, prefers a laid-back atmosphere; and the two frequently come to physical blows over their conflicting philosophies. Other members include Niji, an oboe player who wants to quit unless Sotaro dates her; a teacher who treats the club like a live drama for his own entertainment; and Lucy herself, who harbors a secret crush on Sotaro and a disturbing habit of licking his trumpet mouthpiece. Sotaro, a natural straight man and former athlete with a go-getter attitude, tries to unite the club toward the upcoming competition. The narrative arcs unfold as he first prevents the club from giving up on the competition entirely, then convinces Niji to stay by dealing with her romantic ultimatum. Later, after he successfully brings a majority of members onto the serious side, Kurami warns him that the real apathetic member is right beside him—Lucy, who has been pretending to be supportive only to stay close to Sotaro. The series concludes with the club finding a fragile balance and Lucy’s true motivations coming to light, culminating in a complete but chaotic four-volume run of offbeat club comedy.