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 likely 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 72 of King Solomon's demons -- Shuma being the sole exception for obvious reasons -- who are supposedly controlled by one summoner. Kuruto will show his mother he can do it.
