Blood: The Last Vampire

Saya, a powerful original vampire-hunter, is sent by her liaison, David, to pose as a teenage student at Yokota High School on Halloween to hunt down vampires. Saya must track and kill a Chiropteran that has infiltrated the air base, where she also encounters Nurse Makiho Amano, who witnesses her fight against the powerful demon. As Saya navigates the school, she kills two classmates who are revealed to be Chiropterans, and then saves a third one from being attacked by her own kind. With David's help, Saya mortally wounds the final Chiropteran and disappears with him after covering up the evidence of their encounter.