William Teignin is high flyers of a famous middle school in Britain. In order to pay off the debts left over by the previous generation, he is looking for something to sell at home. He accidentally touched the mysterious magic circle and summoned the demon Grand Duke Dantalion. Even more surprising, William was told by Dantalion that he was a descendant of the ancient king Solomon and had the right to choose the acting emperor of the underworld, and Dantalion was one of the candidates for acting emperor, so in order to let William choose for himself. A youth love comedy began.