Maigahara Senior High, a prestigious music school, has always had a mysterious rumour: if a musical act can perform well enough at the annual school festival, extra credit will be mysteriously added to their report. This piques the interest of Serina Akesaka, a student who, while enthusiastic, is somewhat lacking in the grades department; in response to the rumour, she forms the band Irodorimidori and attempts to earn the mystical extra credit for each of its members.

During the second season of the show, Irodorimidori, in conjunction with Nadeshiko Igarashi, officially re-establish Maigahara's music club. The three new members of the club form a second band, HaNaMiNa, who work alongside Irodorimidori.