Muraki's older, half-brother. They are nearly the same age and look very similar, though Saki has blond-brown hair. Saki was the result of his father's philandering with one of his patients. At about the age of 16, Saki was brought to live with Muraki in their household. Muraki credits this as having ruined his life by destroying his family, his mother going insane and treating him like a doll and for killing his parents. In the anime, Saki is directly responsible for the deaths of Muraki's parents, though in the manga Muraki says he killed his own mother, whether it was to stop her from treating him like a doll or killed her out of mercy due to her going insane from Saki's existence.