Claymore is based on a shounen manga by Yagi Norihiro serialised in Monthly Shounen Jump.
The setting of the story is a fictional world of abundant towns where humans coexist with demons called Yoma. These monsters feed on humans as their main source of food, hiding themselves in human society until they strike. A group from the secret society Claymore vows arise to protect humans that's when the main character comes in while slowly losing himself...