On the night of her 18th birthday, Isabella, an orphan living in the town of Lotsville, didn't know she was a vampire and a human child, and on the night of her 18th birthday, the moon turned blood red, which meant the vampire "Cain" was about to be resurrected. The Holy See dispatched a mission to the head of the Holy Knights, asking him to follow the trail of "Cain" according to the guidance of the Holy Artifact.