Rui was a calm, aloof and somewhat polite individual, rarely raising his voice, and talking with everyone with a reasonable tone and vocabulary, though his guttural way of speaking seems to imply repressed annoyance. Despite difference in demeanor when compared to most demons, Rui was actually a disturbed individual who desired the close bonds that a family had. He was incredibly authoritarian and cruel. Rui was incredibly sensitive to the subject of family. Implied to be Muzan’s favorite.