Demon loses his name and finds this boy (priest?) who carries thr soul of the person who stole his name. He must eat this person to gain his name and power back.... The boy makes a deal with the demon, if he tells him stories of his life, they boy will allow him to eat (have s*x) with him. Thus, the demon and boy start a contractual relationship which ends up becoming more as feelings start to form between the two.
Matsuyoi no Oni