A few years ago, a plague broke out and mankind was devastated. However, the plague does not affect anyone 13 years of age or younger. Vampires keep children.
Lucy and Wilming are among them. When they decided to escape, they were discovered by vampires. Everyone died except Lucy and Wei Ming. The former managed to escape, but the latter was turned into a vampire prop by the vampire. Lucy joins the vampire annihilation force and obtains cursed equipment that can kill vampires. The inevitable war breaks out, between vampires and humans.
Note: This article uses the background of "Seraph of the End" and the characters of "Fairy Tail".