Because of their parent's remarriage, high school student Satou Yuka, suddenly finds herself living together with her stepbrother, 23-year-old high school teacher Satou Taichi. Actually, their parents have not registered their marrriage and therefore they aren't even siblings by law; but since both parents aren't around, they end up living together! Taichi who has a very serious case of sister complex, wishes for Yuka to call him "onii-chan". But Yuka's reaction is very cold?* Contains the short stories titled Private Princess, Chocolate Crash, and Hot Chocolate as extra in each volume scanlated thus far. (Private Princess=vol.1, etc.) To be updated if/when more are released.