Chiaki is a male student at Maron's school, who can transform into "Kaitou Sinbad" , Jeanne's rival, who also collects demons' powers. Maron doesn't realize Sinbad is really Chiaki, but he already knows of her double-identity. At the very beginning of the series, Chiaki moves into Maron's and Miyako's building and transfers to their class, in order to get close to Maron, to stop her from collecting the demons. At first, Chiaki is portrayed as a playboy, whom Maron despises. However, as time passes, he falls in love with her, and he's able to gain Maron's trust, and eventually love, by helping her out of tough situations, and helping her regain her courage--both as Chiaki and as Sinbad. After Chiaki catches Maron staring sadly at her empty mailbox, he begins dropping her "useless" notes, as one of Chiaki's many ways of trying to cheer her. Like Maron, Chiaki lives alone, having run away because he was tired of his father's continuing to marry new women after his mother's death. He later reconciles with his father, after introducing him to Maron.