Mai is a third-year student of the same high school that Yuichi goes to. He met her standing alone in the school building at night, with a sword in her hand. She apparently takes it upon herself to fight and defeat demons at night while the school is deserted. Due to this, she is constantly blamed for accidents because she never denies them, being too sincere to say anything and knowing that no one will believe that there are demons in the school. Her best friend is Sayuri Kurata, the only person besides Yuichi that does not believe that Mai is a dangerous delinquent. Yuichi eventually starts bringing her dinner at the school while she is fighting and during these times Mai begins to warm up to Yuichi. Mai's idiosyncrasy is her unwillingness to carry on a conversation or even to merely utter the meekest of responses when addressed. Due to this, and her reputation as someone who causes trouble, she is most often avoided when at school, and is talked about behind her back. This cold side of her is shown to stem from having very little insight on other people's emotions.

Before Mai met Yuichi or even lived in Kanon's city, Mai was living in a town with her mother who was admitted into the hospital with a serious illness. When her mother is close to death, Mai starts to pray that her mother will be all right and starts to cry on her mother's hand. Miraculously, Mai's mother recovers somewhat by the morning and is soon cured of her sickness. The explanation of this stems from a magical power Mai has within herself. When she cries, her tears carry incredible healing powers which even have the power to bring things back from the dead. The media pick up on this, but Mai starts to get bullied and terrorized as being a freak, so Mai and her mother move to Kanon's city. Ten years prior to the beginning of Kanon's story, Yuichi met Mai during summer break and the two hung out together a lot for the rest of the summer. When the summer break is coming to a close and Yuichi has to go back home, Mai becomes very distraught due to losing a very close friend only just after meeting with him. Mai makes up the story that demons have started attacking the field of barley and that she needs his help to fight them off. Yuichi tells her that he is sorry but he has no choice but to go back home. Mai tells him that she will wait for his return some day.

After starting to hang out with her in high school, Yuichi discovers that Mai has a bad reputation at school due to the events involving the demons. Yuichi tries to improve her reputation by having her and Sayuri attend the annual school dance party, but a demon appears and makes matters worse; during this time, Sayuri even gets attacked. Yuichi starts training with Mai to help her fight against the demons and the two spend a night together at school fighting and destroying them. Mai has been getting hurt with each successive kill of the demons in the form of strange black marks appearing on her body. After an intense battle with the last remaining demons, Yuichi believes he and Mai managed to destroy them all, but Yuichi is later confronted by another demon. He ultimately sees that it is not a demon, but rather a part of Mai's own power that shows him what happened before he met with Mai and what happened after they met ten years ago.

Due to Mai's incredible power to heal things, an adverse affect that she created from this power were the "demons". The reason that she was getting hurt after destroying them is because she was killing off parts of her own self. After Yuichi tries to tell her that it is all over now, Mai stabs herself with the sword and is about to die. Just then, a fragment of Mai's own power materializes before Yuichi in the form of a young Mai and Yuichi reassures her that he will not leave Mai again. Mai's own power saves her and closes the wound she had just inflicted which saves Mai's life. Mai's power believes that now Mai will be able to accept this power that she has. Before Mai's power leaves sight, she asks Yuichi to call her by the name "Hope" (希望 ,Kibō?). Mai is later taken to the hospital where she shares a room with Sayuri and tells Yuichi that she will have to stay out of school until the spring. When spring comes, Mai is able to graduate high school with Sayuri.