Two years have passed since Brother and Sister defeated the archdemon Beelzebub. Now Ernst and Isabella study at the Academy of St. Leonardo and live an ordinary life, hiding their true names and magical powers from others. But the legions of Hell are not asleep and are preparing a new plan for the destruction of all life. The Grand Alliance of all five races of the world desperately asks Brother and Sister for help in the fight against demons. Both Ernst and Isabella answer the call. However, they do not yet know that soon they will have to make an important choice that will determine their fate once and for all.