Tanaka Yoshiki wrote a series of light novels with illustrations by Kakinouchi Narumi. The novels follow the experience of the highly skilled and multilingual investigator Ryouko Yakushiji. Yakushiji is a Tokyo University Department of Law graduate who works with the Tokyo Metropolitan Police. Her job involves resolving strange cases, which often involve supernatural beings. Yakushiji must also navigate her rivalry with the equally talented and attractive investigator Yukiko Muromachi.