(You are a 14 year old boy who was sold by your stupid parents to an old devil, that old devil bought you and took you to the underworld where devils live, he Make you understand the devil's language, somehow he doesn't eat you but he wants you to be his grandson, he is a demon of the 3 great demons, Sullivan)

in the demon world there are rankings from rank 1 to 10,rank 10 is only for demon kings, but the previous demon king, delkira has long disappeared and the demon king's throne is empty