Mairu Shirouzu

Mairu Shirouzu (白水 哩, Shirouzu Mairu) is a third year student at Shindouji Girls' High School, the captain of the mahjong team and their ace for three years.

Appearance
Mairu has dark hair with a clip in the front and twintails in back tied with a yellow ribbon and brown eyes.

During middle school she was taller than Himeko Tsuruta, but some 1.5 years ago the roles reversed. She wears the standard Shindouji Girls' uniform.

Personality
She is usually calm and collected. She has a strong sense of leadership in the team and a strong friendship with Himeko Tsuruta. Mairu is also shown to be quite considerate and astute when thinking about her teammates, as she praised Kirame Hanada for her work in the Vanguard match against Teru Miyanaga and she was able to work out Yoshiko Yasukouchi's thought process in the Sergeant match.

Battling Fujishiro Arc (Toki manga)
The girl appears when Sera talks about going to the nationals.

Final Eight Arc (Achiga manga)
Mairu appears with the rest of her teammates entering the playing hall before the final eight competition begins. In the later parts of the vanguard match, she appears in Kirame Hanada's flashback where she is walking with Himeko Tsuruta, discussing why Kirame got the vanguard position during the tournament. After telling Himeko that she is nothing more than a sacrifice, Himeko wonders why their fifth best player doing that instead. Mariu then says that Kirame doesn't go bust during a match no matter what. Also that it will be up to the remaining four girls to pick up the pieces from her match, unaware that Kirame overheard their conversation. After Kirame's match, she tells her that she did good and now it was Yoshiko Yasukouchi's turn. Before she leaves for her match she says she will get the number two spot. When Hitomi Ezaki returns, she tells her that it wasn't the governments fault but her that lost the points and to leave everything to her. She then tells Himeko that the binds must be extra strict then leaves.

On her first hand, she decides to not bind herself before Seiko Matano begins her move. Mairu realizes that Seiko is up to something but doesn't want to rely too much on what she learned during the second round. Seiko then proceeds to win with a ''tsumo. ''At the start of the east second round, she decides to go with a three han bind. However, Hiroko Funakubo won the round rendering her binds meaningless. She then quietly apologizes to Himeko. With a dealer repeat, she again binds herself this time with two han in hopes to help Himeko if the round should come up during the captains match. Mairu and Seiko battled it out until she intercepted Seiko and won the round. After the win she realizes that that win might be meaningless so she decides to get greedy and go for more. The beginning of the east third round, she decides to go for a four han bind and quickly wins. Mairu wins again during the east fourth round. During the dealers repeat she was the first to get into tenpai and has her eyes focused on Seiko who quickly follows up with her own tenpai until Arata Sagimori declares'' riichi. Arata ends up winning the round and Mairu has to pay most of the points (being dealer and having declared riichi''). The next round Mairu quickly wins with a tsumo. When Hiroko calls a dealers riichi in the next round, Mairu admits that she'd normally fold under the circumstances but knowing she needs the points, she declares riichi; however, Hiroko wins the round. In the second to last hand of the match she decides to go for broke and bind herself with seven han. She then declares riichi along with Arata and ends up winning with a baiman hand. The match ends with Arata winning the last hand. She is then shown watching Himeko's match. Mairu appears when Himeko thinks of how strong their bond is before she wins with her ''baiman. ''When Himeko complains about not getting a key, Mairu says that the starting hand didn't seem possible to win with. Later she watches Himeko and says not to force herself and that Awai Oohoshi is the dealer. After the loss, she is shown trying to comfort Himeko and wonders why Kirame's underclassmen brought her tacos.

National Championship Arc
Mairu along with all the other regulars from Shindouji appear in the playing hall before the Match for 5th to greet the other teams and wish each other good luck. She is seen intermittently throughout the Match for 5th, until the vice-captain's match, where she is the player expected to come out on top. She thinks to herself about the situation, and how despite the much smaller point gap to the top, there's also only 1 hanchan, and winning the average amount of hands she normally does will not be good enough to overtake the top. She strongly wishes to win at least one reservation worth 4 han or higher, and is lucky enough in the first hand to be granted a 3-dora, 2-shanten start. She then swiftly gets into tenpai and wins off of Hiroko, decreasing the distance to the top and completing her 4-han reservation. When the next hand begins, she says that she's really lucky as she starts off 3-shanten with one dora for a chinitsu and makes a 6-han bind, worrying Himeko.

Playing Style/Abilities
Mairu is an extremely skilled player who has been Shindouji's ace for 3 years straight. Her style is to go for fast hands, most likely in an effort to prevent the others from winning and accumulating more points for herself, which energizes more effectively with her reservations allowing Himeko Tsuruta to also win more. She also typically plays a strong defensive game and bails regularly. She is always thinking about the point difference and is very accurate in predicting how her hand will come together.

In addition to her basic skills, she has an ability that must be used in tandem with Himeko. Her ability is called reservation. Looking at her starting tiles, she determines possible yaku and han values within her grasp, sets a minimum han value to reach, then she must place her tiles face-down before opening them again. If she wins with that hand with the amount designated, 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. She doesn't have to set a han limit every had and if she doesn't than her and Himeko's winning hands will be unrelated. When counting han, she can use dora in the count as well.

In the 71st Mahjong Interhigh Semifinals, Mairu puts down her usual style of play: not only did she chase a dealer's riichi, she went for much larger hands, to the point of passing up cheaper waits when in riichi (hence putting her in furiten) in order to make larger dents in the point difference. Seiko Matano calls her a "true ace," speculating that Shiraitodai's number 5 (who can beat prefectual aces) could not beat Mairu.

Etymology

 * The name Mairu means "miles" (哩).
 * Mairu's surname Shirouzu means "white" (白) (shirou) and "water" (水) (zu).

Trivia

 * Mairu shares a dorm room with Himeko Tsuruta and Mairu has been together with her ever since middle school.
 * Mairu has been the ace of Shindouji Girls' High School for three years straight.
 * She shares this trait with Teru Miyanaga who has also been the ace of Shiraitodai High School for three years.
 * Despite Seiko Matano saying that Mairu was a "true ace", Mairu says that she failed to perform well enough in the 70th interhigh, and presumably the 69th interhigh as well.
 * This is accentuated by the fact that while Shindouji is a popular school due to finishing well in the Inter High most of the time, their exact placement is never mentioned (compared to Senriyama Girls' High School or Himematsu High School who's spot in the National ladder is always mentioned at 2nd and 5th, respectively).