In order to inherit the will of his father, Kumagoro Teino (voiced by Riki Koyama), high school student Masago Teino (voiced by Takahiro Sakurai) entered the aristocratic school Shinryuin Academy to learn how to become a qualified president. Not only that, in the next two years, Masago must find a lifelong marriage partner in the academy. This stumped Masago, who has an ordinary personality, but there is nothing difficult in the world, and Masago's happy high school life is about to begin. On his birthday, Masago received a call from a girl who claimed to be his "sister", but Masago had no idea who this sister was. In the academy, Masago met many cute girls, including the class committee member Tsuru Shinnoshin Noeda (voiced by Natsuki Ishihara), the silent and shy Kaminagi (voiced by Ayane Sakura), and the high-IQ girl Sagara Mei (voiced by Rina Hidaka), and Masago felt that the mysterious sister was hidden among these girls as soft as flowers.