Blood +

From Animepedia

Blood + is a series related to the movie Blood: The Last Vampire.The story revolves around Otonashi Saya, a highschool girl, who lives a peaceful life with her family, though she has no memories of her life beyond that of the past year.However she becomes invoved in a war that has been raging on through the passage of time, influencing the modern world.There are two groups in the ensuing war.The first group consists of immortal monsters called Chiroterans who can change their appearances into that of human beings.These monsters feed on the blood of the living.The second group is an organisation known as the "Red Sheild" formed to hunt down the chiropterans and kill them.