Following the demon lord Hadlar's downfall, monsters break free from his control and find refuge on the tranquil island of Delmurin. Dai, raised by the gentle monster Brass, aspires to become a hero. His chance arises when Hadlar resurfaces, prompting the legendary hero Avan to train Dai for the looming conflict. However, Hadlar, now serving a more menacing demon lord, targets Avan. In a desperate bid to protect his disciples, Avan sacrifices himself in a futile attempt to defeat Hadlar. As Dai and his fellow student Pop face imminent danger, a mysterious mark manifests on Dai's forehead, granting him extraordinary powers to repel Hadlar. United by a common goal, Dai and Pop embark on a quest to avenge Avan and restore harmony to their world.