Blood-C (2011)

Saya Kisaragi is an outwardly normal girl who serves as the shrine maiden to a country town; in reality, she is a skilled swordswoman charged by her father to defeat Elder Bairns, monsters who feed on human blood. As her battles grow more desperate and more people she cares for fall victim to the Elder Bairns, Saya begins finding faults in her reality, and eventually uncovers a disturbing truth about herself, the town and her surviving friends.