Since childhood, Tsukasa grew up in the royal family of wizards, from generation to generation the Tenma dynasty passed the magic staff to adult heirs.The younger generation had to follow a number of rules. The first and most important rule is not to meet monsters in terms of love relationships. When Tsukasa's parents died, he came to their grave every Sunday, which was located on a remote island that could only be reached by boat. One day, as always, he was cleaning up and saw a boat sailing away. Suddenly, behind his back, he hears that someone is approaching him, and notices Rui, the son of Satan himself, next to him. "Rui... How did you end up here?"