In an indistinct future, humans and vampires are allied against the savage demons that relentlessly attack their cities.

In the fortified town of Newhaven, a centuries-old vampire, Wilhelm, is slowly losing track of why he fights. Meeting the human child Ariadne and watching her grow up to become a fierce fighter reminds him of his purpose and gives a face to the humans he tries to protect.

As years pass, however, and Aria becomes a young woman, then a vampire, his protectiveness slowly turns into love...