A 16 year-old first-year high school student who becomes involved with the Shibuya Psychic Research (SPR) after she accidentally breaks an expensive video camera that was being used by the SPR in an investigation of an old building at her school. In the same incident, she is saved from a falling bookcase by Lin Koujo, who is injured instead; to repay her debt, she fills in for Lin to assist SPR's manager Kazuya Shibuya. After the conclusion of the first case, she is offered a paycheck for her work and a part-time position at the SPR. As the series progresses, it is revealed that Mai has ESP abilities, which include astral projection, psychic dreams and clairvoyance.
Cute Clumsy Girl: Not so much emphasized, but she has her clumsy moments. The most clear example is when she breaks Lin's camera on the first arc.
Demonic Possession: In the Silent Christmas episodes, after John exorcises a spirit out of a young boy, the spirit goes into Mai and possesses her until the end of the arc.
It happens again in the Bloody Labyrinth arc, when she gets possessed by the spirit of one of the maids that was killed in the mansion. The spirit makes her experience her death in what's probably one of the most terrifying moments of the anime. The spirit possesses her again later but Masako notices and effortlessly exorcises the spirit out of Mai's body and lays it to rest.
Near Death Experience: In the seventh arc, she has a vision of what it was like to be murdered, when one of the spirits that was killed in the house possesses her and makes her experience her murder on her own flesh.
And later in that same arc, when she goes to rescue Masako. She's saved by Lin just in time, though.
Tempting Fate: Near the end of episode 10, Mai muses about how it would kind of suck to have psychic powers, and that she's glad she's just an ordinary high school student. Guess what we eventually learn she has?
What the Hell, Hero?: Mai is not pleased to discover that Naru is willing to turn a death curse onto six hundred relatively innocent students (hoping that the curse would dilute itself and "merely" severely injure them rather than kill them. Maybe) just to guarantee the life of one Jerkass teacher — his justification being that, unwittingly or not, they still invoked a powerful death curse. Naru instead takes a third option and diverts the death curse to six hundred hitogatas of innocent students, leaving everyone unharmed.
A 17-year-old paranormal researcher and the manager of the Shibuya Psychic Research center. Mai nicknames him "Naru" for his narcissistic (narushisuto) attitude; this nickname generally comes to be adopted by their colleagues. Though appearing cold and critical in front of his friends, he does care for them deeply and earns their trust and respect. Eventually, it is revealed that Naru is actually the famed paranormal researcher and psychic, Oliver Davis, and that he has very strong psychokinetic abilities.
All There in the Manual: There are several things about Naru that are either vaguely hinted at or not brought up at all in the anime but are explained fully elsewhere.
And in the final volume of the manga, SPR discovers that "Shibuya Kazuya" is apparently only an alias for Oliver Davis, a famous British parapsychologist.
Psychic Powers: At the end of the eighth arc, Lin reveals to Mai that Naru has an outstanding amount of psychic powers, too much for his body to control, and that it was what caused him to pass out after briefly using said powers.
Unspoken Plan Guarantee: He may tell Lin his plans, but that's only because he needs his abilities. Except for that, he rarely reveals his plan, and Mai and the others have to figure it out on their own.
An outspoken 23-year-old self-styled shrine maiden whose powers and knowledge often come up short compared to the other practitioners in the earlier arcs. This is due to her powers deriving from tree spirits and SPR's earlier cases being in urban areas. She is also a licensed doctor at hospital, a talented cook and quite wealthy.
The Chew Toy: She is often the object of tease (mainly from Naru and Monk) due to her rituals not being very effective in the first few arcs.
Conditional Powers: Her power stems from her connection to tree spirits and is stronger when in rural areas. Unfortunately until the final arcs all the investigations occur in urban areas, so her powers are greatly limited until then.
Shipper on Deck: For Naru/Mai. On episode 11 of the anime, when Masako suggests that they should divide in couples to attract the spirit, he whispers to Mai that it was her chance to get a date with Naru.
Near Death Experience: On the very first arc. The roof was falling down on the room he was practicing an exorcism, and it would've ended him had Mai not warned him and gotten him out of there just in time.
Demonic Possession: On episode 11, although it's more or a comic relief situation. It is more serious on the eighth arc, when she summons the ghost of a person who was recently killed in order to find out who killed her, and of course, said ghost takes full control of Masako's body to talk to the group.
Near Death Experience: On the third arc, a spirit pushes her down the stairs of the school while she was searching on her own. She was found by the others and taken to the hospital by John soon enough though.
Not to mention when she's abducted near the end of the seventh arc. Mai finds her and attempts to free them, but is captured too, and both are almost killed by the Big Bad (in a quite horrific way, might be added), but they're saved just in time by Lin.