Reiji Tokisaka

A private detective that specializes in particularly brutal murder cases. Was formerly a detective in the police force, but quit after he lost his fiance. Lives together with his little sister Yukari. Doesn't stay at home much because he puts his work above everything else. Loves to pore over history books whenever he has free time. Infiltrates Ouba Girls Academy as a substitute history teacher.

(Source: vndb.org)