WAIT I HAVE A BAD MEMORY WHY IS HE CURSED?

Mei (full blood vampire who turned sayo to a vampire) casted this curse on him because he wants to become a vampire so mei made a deal with him: make sayo kill mei or he will be dead. Sayo has to kill mei or the curse will overtake yamadare and he will be dead. Sayo cant hurt a fly but he also cant let yama die so he has to figure out a way to kill mei. If mei is killed, yama's wish to become a vampire will be fulfilled if not then he dies.