Summary -
There are two worlds, one for demons, "Gehenna," and the human world, "Assiah." Demons possess humans and other creatures on Assiah to create havoc and destruction here. The only ones who can fight the demons are exorcists. The story starts off with a teenage boy named Rin in a church. His foster father the head priest (or something like that) at the church. After a couple of events, Rin sees and finds out there are demons in the world, his foster father and his followers are exorcists and... Rin was actually the child of Satan. His foster father sacrificed himself to save him from Satan. Then he swears that he shall avenge his foster father by becoming a exorcist... and kill Satan.
