Kyungsoo was just a boy, young naive and innocent. Kai was a king, the king of the underworld. When Kyungsoo's father becomes ill with a deadly disase, Kyungsoo panics, unintentionally summoning the king of the underworld, a demon named Kai. In his haste to heal his father before it's too late, Kyungsoo strikes a deal with Kai, therefore becoming the demon's wife.