Mio serves as a companion to Yakko Sakazaki, who has experienced a supernatural experience after doing a seance with Mio to commune with a dead schoolmate. This event coincided with a conspiracy to amplify paranormal events, surrounding seven mysteries associated with the Honjo area. A recent transfer to Yakko's school, Mio is later revealed to have experience with the supernatural, working with the police to help investigate paranormal matters. She also assists Yakko with her struggles.