The Demon King finally revealed he is actually alien sent here for invasion. Unfortunately he is alone, and can only rely on the native monsters for his army. Those are too weak against the magical weapons used by human. After using body of the Mage, she spread magical stones to the atmosphere, rendering magical weapons useless. Now, without power of magic by the human's side, the Demon Lord used the summoning circle to call force from her own planet.

Finally, she offered the Hero. He can either fight, and try to destroy the summoning circle, which will make it impossible for Demon King to call for more reinforcement. Humanity might win. Or, he can ask to be returned to his own world, the thing he had been wanting for.