After the demon lord Hadlar is defeated, the monsters released from his evil will relocate to the island of Delmurin to live in peace. Dai, the only human on the island, has been raised by the kindly monster Brass and dreams of becoming a hero. His wish becomes reality when Hadlar is resurrected and the former hero Avan arrives to train him for the impending battle. However, Hadlar declares that he now serves an even more powerful demon lord and turns on Avan. To protect his students, Avan unleashes a Self‑Sacrifice spell, but it fails to defeat Hadlar. As it appears that Dai and Avan's other student, Pop, are doomed, a mark appears on Dai's forehead and he suddenly gains superpowers.