The heir to the Kaburagi Corporation receives a visit from the family lawyer bearing his late grandfather's final wish: that he attend an all-girls school. With the help of his fashionable childhood friend Mariya, Mizuho enrolls and navigates the new environment. An early misunderstanding snowballs until he is elected the school's "Elder Sister" — the idol of the entire student body. Maintaining his identity for the rest of the year may be the hardest thing he has ever done.