Mami wants revenge on Ran, and Yuya is thinking of a way to get Ran to be his girlfriend. When Ran invites him to the pool, he jumps at the chance, dragging Rei with him. Just when all seems well and good, Ran's little sister Sayo and her boyfriend Masato appear on the scene. They are both eager to become police detectives. Mami and Harue jump at the chance to take over Shibuya while everyone is away.