OP: “Raison Dâ€™Ãªtre” by Nightmare
ED: “Danzai no Hana~Guilty Sky” by Riyu Kosaka
Story Overview (from Wikipedia because I have no free time for my own written summary):
The setting of Claymore’s story is a fictional world with medieval technology. Politically, it appears to consist of a large number of scattered, apparently independent, towns. In this world, humans coexist with creatures called Yoma sentient monsters that feed on human innards. The Yoma, being shape-changers, can take on human form and live in disguise amongst humans. By consuming the humans’ brains, 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.