The story begins with a young boy named Dai remembering a story told to him by his adoptive grandfather, the monster magician Brass, about the defeat of the Demon King Hadlar by the hands of a hero known as Avan. After the defeat of the Demon King Hadlar, all of the monsters were released from his evil will and peace reigned supreme around the world once again for ten years. Some monsters and demons moved to the island of Delmurin to live in peace. Dai, the young protagonist of the series, is the only human living on the island. Having been raised by Brass and with his best friend, the monster Gome, Dai grows up dreaming of becoming a hero.