Trouble is stirring in the Underworld. A large group of strangely powerful demons have started an empire. Demons are not supposed to bring people to the Underworld. There are other forms to do that work. Ace needs to get to the leader of the empire to take him down, but he needs more information first. Ace needs help to be able to take back his throne at the top of the Underworld and sort out his growing feelings. Ace knows he can't get to the demon palace on his own, so he calls up a few friends and his demon queen sister.