On the surface, Saya is a stunning 16-year-old, but that youthful exterior hides the tormented 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 hunts.

In Japan, the vampire-hunter Saya, who is a powerful original, is sent by her liaison with the government, David, posed as a teenage student to the Yokota High School on the eve of Halloween to hunt down vampires. Saya asks David to give a new katana to her. Soon she saves the school nurse Makiho Amano from two vampires disguised of classmates and Makiho witnesses her fight against the powerful demon.