In order to protect her most important sister, Margaret did not hesitate to agree to the ruthless vampire prince and transform from human to vampire. When people around him learned that Margaret had become a vampire and left one after another, only the man who had been eager to protect him since he was a child was willing to stay. Even if she could turn into a vampire at any time, she would not hesitate. But Margaret, who has immortality, insists on taking on everything by herself. Such stubbornness makes the vampire prince find it extremely attractive! How much can humans and vampires pay for an important person?