Fushiou no Musuko

"Hey... What kind of meat is this?" Set in modern-day Japan, though it's a world where supernatural beings like werewolves and vampires live quite normally. A sixth-grade girl named Yukiko, who is preparing for her junior high entrance exams, suddenly gets a new transfer student in her class. The boy, who introduces himself as Fushio Yamada, is actually the son of the Immortal King. One day, Yukiko is attacked by a man-eating monster while trying to save a classmate, but is rescued by Fushio. However, as the price for saving her life, Yukiko ends up no longer human, but an immortal being herself.