Yoruhiko is a sixteen-year-old boy who spends most of his time indoors, immersed in trading card games and self-taught "assassination techniques." His twin sister Akane, by contrast, is lively, popular, and fiercely committed to perfect school attendance—she believes that if she never misses a day, her withdrawn brother might eventually be inspired to come to class himself. One summer day, Akane chases a dropped rice ball into a river, hits her head, and falls into a coma. Faced with the imminent ruin of her attendance record, Yoruhiko decides to take her place. He dons her sailor uniform and enrolls at the all-girls boarding school, Peach Garden Academy.

Once inside, Yoruhiko must maintain the disguise while navigating a dormitory life far outside his comfort zone. His first challenge is his sister’s roommate, Mashiro, a gentle airhead with a massive bust and a dream of becoming a nurse; she quickly grows attached to “Akane.” Two more classmates soon orbit around him: Yuyu, a boisterous rich girl who peppers her speech with “ssu” and shares Yoruhiko’s love of the trading card game Duel Masters, and Hojo, a studious, glasses-wearing girl who has a pathological fear of boys and unwittingly finds herself drawn to “Akane.” One by one, these girls discover Yoruhiko’s true identity, yet rather than expose him, they decide to help keep the secret—often resulting in comedic, heartwarming, and occasionally risqué situations.

The story follows a series of episodic arcs: the school festival, a sleepover for a manga-drawing collaboration, and a Christmas party, all while Yoruhiko struggles to balance his growing bond with the girls against the constant threat of exposure. The tension peaks when the entire school learns that “Akane” is actually a boy, forcing him to face the consequences of his deception. In the final arc, the girls stand by him, and the manga resolves with a warm, happy ending that affirms the connections forged through this unusual charade.