Lt. Kozu Karina is a member of the Tokyo Police Department's 'U' Division ('U' standing for 'unknown’'or 'unexplained') and is in charge of investigating unusual cases, as well as an employee of Phantom Quest Corp. As Ayaka Kisaragi's contact within the department, Karina often supplies her with important clues to the various cases she is involved in.

Karina also has a romantic interest in Ayaka, as well as trying to protect her either from the supernatural threats Phantom Quest Corp runs into from time-to-time, as well as being a touchstone appealing to her common sense. He also tries to protect Ayaka from herself – namely her destructive habits of excess drinking and overly-exuberant shopping. He also drives an old Volkswagen Beetle, which often breaks-down at the worst possible times!