Mairu Shirouzu is a third year student at Shindouji Girls' High School and captain of the mahjong team. She has been together with Himeko Tsuruta since middle school. Her ability is called reservation. First she imposes a restriction on herself the moment she opens her hand. If she wins with that hand then Himeko will win that same round with double that amount. If she doesn't win then Himeko will almost never win. If she doesn't link with Himeko then their hands will be unrelated. She can use her ability with yaku or dora. Mairu says that her usual style of play is to go for quick hands worth around 3900 pts.