She's a middle school student and the daughter of Kouzou Tahara, the only survivor from Hell's Gate. There is significant emotional detachment between Mai and her father and Mai chose to adopt her deceased mother's maiden name. As a result of her father's attempts to subdue her Contractor powers, she became a Moratorium but eventually reverts to a Contractor. Her power allows her to create and manipulate fire. Her remuneration takes the form of humming a song. She seems to think of Hei as an older brother.

Source:Wikipedia