The Gretchen family is a high-ranking vampire family that is called as the guardian of wisdom and the pursuer of knowledge. They have poured their efforts into the study and knowledge of magic for centuries. While they were the distant relatives of the princess Lewisia, they always have upheld the rule of not interfering with the humans, as they believed humans were fools who were swayed by greed. But when the current head of the family, Vilhelmina La Gretchen, married a human, their immense knowledge that was concealed for centuries finally became accessible to humans. Barsi, the human who married Vilhelmina and took on her surname, was an alchemist of the Tower of Sage.