*After the main (Elis) route of the prequel*
Tatsuya, Marie and Saya returned to their world after defeating the armies of the Goddess in Cielo Pantasia. However, Tatsuya, on a whim, pulled Elis into the magical circle while they were teleporting, so now the four of them are at Tatsuya and Marie's house, with their parents.
There Tatsuya tells them that he thinks of leaving this world once more and remain in Cielo Pantasia to live there with Elis, everyone is surprised, but accepts it. Then Tatsuya tells Elis that as she had promised before, he wants her to make him the new Maou, and after making her agree in the bed, they return to her world. There, in front of a huge crowd of Demons who came to welcome Elis, Tatsuya shouts he is the new Maou, but of course none of them agrees with it. So in the end Elis decided to have all the Demon leaders battle each others and the winner should be the new Maou, also, the Oracle Knights see this as a chance to fight Tatsuya once more, fair and square, so each of them decide to lead their own armies.
Now Tatsuya has to fight all these enemies to add them to his army as he did before, because for now he can only count on Elis and Amoe. And he intends to show all of them who is worthy of becoming the new Maou!
The only good thing is that he won't have to fight Marie and Saya because they remained in their world... or did they?