Таніяма Май

She is 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. She refers to Shibuya as Naru due to his narcissistic nature.

As the series progresses, it is revealed that Mai has ESP abilities, which include precognitive dreams and clairvoyance. Mai also demonstrates an instance of astral projection, when she gives Masako a key to comfort her after she is taken by a monster. In Mai's dreams, Naru frequently appears to guide her.