白水 哩

Mairu is a third-year at Shindouji Girls' High School, captain of the mahjong team, and their ace for three years. She has been together with Himeko Tsuruta since middle school. Mairu is usually calm and collected. She has a strong sense of leadership in the team and a strong friendship with Himeko. Mairu is also shown to be quite considerate and astute when thinking about her teammates.

Mairu's ability is called reservation and can only be used with Himeko. First she imposes a han restriction on herself the moment she opens her hand, such as 2 han or 3 han, then she must place her tiles face-down before opening them again. If she wins with that hand with that amount, or higher, then Himeko will win that same round with double the han she set. If she doesn't win then Himeko will almost never win and if she does it's likely to only be worth 1 han; if Mairu wins with more han than the amount she set, Himeko cannot use the extra han. If she doesn't link with Himeko then their hands will be unrelated. When counting han, she can use dora in the count as well.