A new student in Maron and Miyako's class who also lives in the apartment next door to Maron. Prior to the start of the series, he ran away from home. Like Maron, Chiaki also has an alter ego, Kaitou Sinbad. Although he always seemed to go against Maron, he does it for a reason. He also knew about Maron's true identity. Chiaki is a "ladies man" or "womanizer" and always tries to seduce Maron, who at first, can't stand him and his habit of always trying to protect her. At first, he says he was just trying to get closer but later he says he wants to protect her forever.