The king eats everything in the world

One night, high school student Komatsu Yukari is attacked by a bizarre assassin named Portaombrelli. Before death strikes, the young man is saved by a strange woman who introduces herself as the 'Evil King', a being whose goal is to devour all the evil in the world. That being has the same appearance as Komatsu's older sister, Karen, who was recently killed by Portaombrelli himself.