Zero is a witch who is ignorant of the world and travels with a half-beast half-human mercenary who longs to be human. Witches who practice sorcery exist in the world, however, in this era no one knows how about the art and study of witchcraft. Zero is going on a journey to search for a magical tome called "The Book of Zero" that hides a power that can destroy the world. The mercenary travels with her as her guard.