Despite her gyaru looks, Aihara Yuzu is an innocent high school girl with no experience and no prior loves. When her mother remarries, she's transferred into the prestigious "Aihara Academy" for young ladies. However, on her first day at school she happens to witness the diligent student council president, Aihara Mei, making out with her hot homeroom teacher... Yuzu returns home, unable to hid how upset it left her, when her mother announces Mei will be her new step sister, and they'll be sharing a room...?!