In this world, humans coexist with creatures called Yoma (妖魔?) sentient monsters that feed on human guts. The Yoma, being shapeshifters, are capable of taking on human form and living in disguise amongst humans. By consuming a human's brain, Yoma can also absorb their memories, allowing them to disguise themselves as specific people without alerting any of their close friends or family.
A nameless and highly secretive organization has created an order of superhuman warriors to protect humans from the Yoma. These warriors have come to be popularly known as Claymores, after the immense claymores they wield. Villages being attacked by Yoma hire Claymores to kill the Yoma for a large fee.
This organization creates the Claymores by implanting Yoma flesh and blood into humans, thus creating hybrids that are more powerful than the original Yoma, in addition to their weapons training and often greater intelligence. These hybrids use large claymore swords that normal humans lack the strength to wield and are characterized by their silver eyes and light-blond-to-white hair. A Claymore's standard abilities include overall enhanced physical prowess (most noticeably, strength), faster healing, limited shape modification and the ability to detect Yoma by sensing their Yoki (妖気?). To use their special abilities, they access the powers of their Yoma-half. However, if the Yoma powers of each Claymore are pushed over a certain limit the Claymore loses all humanity and becomes a powerful, highly intelligent, and incredibly bloodthirsty Yoma called an Awakened Being. A Claymore will ask a friend (usually a fellow Claymore) to kill them if they sense they are "Awakening", ensuring that they do not turn into the very monsters they hunt.