A 16 year-old orphan and first year high school student who temporarily fills in as an assistant for SPR to repay her debt when she accidentally injures Naru's regular assistant, Lin, and breaks a camera that was being used in an investigation of an old building at Mai's school (It is later revealed that the camera was covered by insurance, and the reason for her employment is unknown). After the conclusion of the first case, she is offered a regular part-time position for SPR and acts as an office and on-case assistant for SPR after developing an interest in the handsome boss of SPR, Shibuya Kazuya who she nicknames Naru for his narcissism. She openly dislikes Naru for his egotistical attitude and often argues with him, but harbors romantic feelings for him as well. She believes that her attraction to him manifests in her dreams as he often appears in them smiling and supporting her. It should be noted that both her parents have died: her father when she was little, and her mother when she was in middle school. Mai was taken in by a teacher who helped her through those years, yet when she reveals this late in the series, she is living alone and supporting herself through her wages at SPR.

A paranormal researcher and the handsome 17 year-old president of the SPR, Shibuya Psychic Research. His nickname "Naru" is short for "narcissist", given to him by Mai. Contrary to the other characters, he does not appear to possess any kind of spiritual power, and must count on his companions' abilities and his own intellect and knowledge to solve the cases they investigate. It is later revealed that Naru is an extremely powerful psychic, but using it takes a toll on his body because it is difficult to control and can only be used as raw power.

Though appearing cold and critical in front of his friends, he does care for them deeply and has earned their trust and respect. He and Mai apparently share a close relationship as she is the only girl he addresses by given name, unlike Ayako (Matsuzaki-san) and Masako (Hara-san), resulting in the latter becoming jealous of Mai. When Mai notices that Naru treats her differently from their friends, she becomes angry and confronts him; Naru only smiles to indicate she is special to him. It is uncertain if he likes Mai romantically. "