Yuzu Aihara, a carefree city girl, transfers to the strict all-girls Aihara Academy after her mother remarries. On her first day she clashes with Mei Aihara, the cold student council president who enforces the school's rigid dress code. That evening Yuzu learns that Mei is her new stepsister and that the two now share a bedroom. Forced into close quarters, Yuzu's irritation with Mei gives way to feelings she never expected.