The "grimoire fantasy" series follows a witch named Zero who is ignorant of the world and 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.
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(Source: Anime News Network)

Also goes by the names Shintaro Ohata and Shintarou Oohara.

Furugiya no Tenshu