Mai is shown very friendly at times and likes to tease him for having lot of knowledge calling it useless knowledge and also calling him useless for battles, but she is seen to praise him sometimes. It is yet to be revealed how they met or formed a team in the first place. Mai trusts and cares for Haruhiko very much and very much is the same for Haruhiko. They both call each other by their first names, though Haruhiko calls her Mai-senpai. Mai has feelings for Haruhiko.
She starts to show jealousy from Episode 5 when Haruhiko was paying all his attention to Koito. She herself gets easily embarrassed when Haruhiko tries to act cool towards her when they are together by themselves. After she gets embarrassed she teases him saying that he is being snotty and pretentious. Mai's feelings for Haruhiko begin to blossom after Episode 8 when Haruhiko saves her from being assaulted by the phantom monkey. She starts to show a huge respect for Haruhiko's powers, and is endeared by his care for her.
When Mai takes care of Haruhiko as a child in Episode 11, she gains a better understanding of Haruhiko's past and relates to his lonely childhood, protecting him and being the motherly figure that he's always longed for. After Mai reads the essay that Haruhiko wrote as a child, she comes to terms with how much she cares for Haruhiko, and wants to make sure that he never feels alone again.
Their similar childhood often brings them closer together. They both shared the same perspective on lifestyle, and both believed that living alone was always the better alternative. Over time through their experiences with their friends and each other, they have grown to appreciate their relationship and relationship with others. Haruhiko comes to understand that Mai is just like him and is often subjected to loneliness. After seeing her change to believe in others, Haruhiko has gradually fallen in love with the blonde, and has too learned to treasure those he cares about.
They both are very friendly and open with each other and became friends very quickly, and they have like a sister-bond, since Reina says that her older sister who moved away reminds her Mai very much. Mai always praises Reina for her abilities and trust and cares for deeply- Reina sees Mai as a older sister, calling her onee-sama. Despite having a very close bond, Mai can get jealous when Reina and Haruhiko gets too close to each other.
Their relationship starts off as a negative one, and Mai claimed that Koito got on her nerves sometimes. Mai also got annoyed at her for being so rude to her, especially since Mai is an upper-class men. However, their relationship improves as the series progresses, with them becoming very good friends and calling each other by first names. They were also seen to hug and hold hands, and Mai cares for her and their coordination is quite good as both of them is very skilled at fighting, and Mai knows that Koito's ability is very useful. They are on good terms.
Mai immediately likes Kurumi and thinks her ability is very good and that it could help her team out. Mai is also seen to worry about her well-being since she is the youngest in the group.
Mai and Ruru are on friendly terms, and Ruru affectionately calls her "Mai-cchi". Mai is the one who have known Ruru the longest of the girls, and Ruru is usually by Mai's side when Haruhiko isn't nearby. Mai has also shown to care for Ruru, and became very worried about her when she passed out in Episode 12.
Mei is Mai's younger sister. They argue and fight a lot like siblings do, but it seems like they do care for each other.