In the prestigious Azrael family, known for producing many individuals with magical powers and Holy Knights, the second son, Rinda, also aspired to become a Holy Knight. However, he possessed no magical abilities, making that path unattainable for him. Further burdened by the loss of his parents, Rinda spends his days engrossed in household chores, playing the role of a parent to his younger siblings. One day, an extraordinary change occurs in Rinda: he grows sharp fangs, horns, and even small wings and a tail—taking on an appearance resembling that of a demon. Confused by this transformation, he decides to seek help from his elder brother Fang, who lives alone as a Holy Knight. It is there that Rinda learns a shocking secret about himself.