Demon 72

His name is Kuruto Kagemitsu -- a cute boy with a vengeance. The demon's name is Shuma. He was summoned, much to his surprise and chagrin, by that cute boy...and forced to be his servant. Their goal - one intrinsic and the other quite extrinsic - is to eliminate 71 of King Solomon's 72 demons (with Shuma being the sole exception for obvious reasons), who are rumoured as being controlled by a single summoner.