Kimito Kagurazaka is an ordinary guy with an alleged obsession with muscular men—or at least, that's the false story he's forced to maintain to avoid trouble at Seikain Academy, an elite all-girls school. Abducted by the institution under the mistaken belief that he is attracted to men, Kimito becomes their "commoner sample," meant to introduce the students to both common life and male presence so their eventual transition to the outside world won't be shocking. Threatened with castration if his true preferences contradict the school's assumptions, Kimito keeps up the charade to safeguard his masculinity.
However, eccentric individuals lurk everywhere, complicating Kimito's existence further. Among them are Aika Tenkuubashi, a social misfit who speaks without a filter; Hakua Shiodome, a child prodigy; Karen Jinryou, a samurai's daughter obsessed with defeating Kimito; and Reiko Arisugawa, the perfect student who harbors fantasies of marrying him. Together with the commoner himself, these four girls form the Commoner Club, aiming to educate the students about life beyond the school walls, while Kimito gradually uncovers the peculiarities of the girls surrounding him.