Hypnos is a demon of the Spirit Family who must sleep 20 hours a day; due to this, Princess Suya regards him as a master in the art of sleeping. He prefers to hang out in the Old Demon King Castle simply because it is more quiet there. When Tasogare, Poseidon and Hades were young, Hypnos is seen looking the same age as in the present. One time, he covered for the three when they broke a statue while playing.