Dragon Quest: Dai no Daibouken (1991)

Dragon Quest Dai no Daiboken

Dragon Quest: Great Adventure of Dai

ドラゴンクエスト ダイの大冒険

It starts with a kid named Dai remembering a story told to him by his grandfather, the monster magician Brass, about the defeat of the Demon Lord Hadlar by the hands of a hero who, as the story progresses, is known to be Avan.