Buster is one of the angels. There has been a fight going on between Angels and Demons for ages but lately, thşngs were getting much more intense. Demons would sneak in the gates of heaven and hunt down Angels or pull them down to hell.

After the Archangel solution to stop the demons, Buster was commissioned as a guard angel. Angels raided down the hell and catch a few demons, neutralized them and locked them into a execution room. Buster was no longer responsible, so he just start walking away from the execution room to report things to the arcangel until he heard a familiar scream inside the room. He paused.