She is biologically male, and states that God placed her in the wrong body. Prefers to be called Seiko instead of Seishiro because it sounds more feminine. Gave Otani his first kiss, but he later found out she was physically male when she took off her shirt when tending to his injury in the school infirmary. She was afraid that Otani would think she was disgusting, but Otani stated that he didn't think such a thing and they remained friends.
