10 years ago there was an explosion that broke seals of the demon world... that time demons came to the human world. To keep them away, special wards were created, which kept demons in one place... but not only demons.. also humans who survived the explosion were imprisoned there. A few years after the explosion, a special delegation was sent to check inside the ward, and to save humans left there... but there were no longer any humans... there were ouma... fusion of demon and human that could use demonic powers while having the rationality of humans....
Sleeper is a band which has 6 members... among them there is Mika, whose powers are not know yet and Row, who sometimes can't hold his demonic nature... this is their story...