On the surface, Saya is a stunning 17-year-old, but that youthful exterior hides the tormenting soul of a 400-year-old "halfling." Born to a human father and a vampire mother, she has for centuries been a loner obsessed with using her samurai skills to rid the world of vampires, all the while knowing that she herself can survive only on blood like those she haunts. When she is sent onto an American military base in Tokyo by the clandestine organization she works for, Saya immediately senses that this may her opportunity to finally destroy Onigen, the evil matriarch of all vampires. Using her superhuman strength and her sword, she begins to rid the base of its evil infestation in a series of spectacular and elaborate showdowns. However it is not until she forms her first human friendship in centuries with the young daughter of the base's general that Saya learns that her greatest power over Onigen may well be her ability for human connection ....