Immortal Vampire

He is the youngest Duke of the vampire clan. But fate made him have an irrevocable contract with a girl with half human blood. She loves the girl deeply but doesn't know it. The girl's unusually rare foundation brings her numerous dangers. Only by constantly increasing her strength can she protect herself and the people she loves. But when she thought she could protect herself, she found that what was standing in front of her was a fog. How will the two of them develop in the end?