From Dark Horse:
Suffering from extreme amnesia, high school student Saya Otonoshi can't remember anything from her life beyond the last year. Living with a foster family outside a military base in Okinawa, Japan, Saya's attempts to live a normal life are shattered when a Chiropteran, a horrific vampire-like monster, attacks her. Saved at the last minute by a mysterious man named Hagi, Saya is presented with a sword that awakens in her a warrior's skills and bloodlust and sets her on a course that will lead her to the answers to her missing memories, and into battle against a race of creatures intent on destroying the world.