"Dragon Quest: The Adventure of Dai" is a fantasy anime series based on the manga by Riku Sanjo and Koji Inada, which itself is inspired by the popular "Dragon Quest" video game franchise. The story is set in a world where humans and monsters coexist, initially under the rule of the evil Dark Lord Hadlar. After Hadlar is defeated by the hero Avan, peace is restored, and the monsters retreat to the island of Dermline. Dai, the protagonist, is a young boy raised by the kindly monster Brass on Dermline. Dai dreams of becoming a hero like Avan, despite his humble origins.

The peace is shattered when Hadlar is resurrected by the even more powerful Demon King Vearn. Hadlar declares war on humanity, and the monsters of Dermline are forced to serve him. Dai discovers he possesses the mark of the Dragon Knight, a legendary warrior with immense power tied to dragons. With the guidance of Avan, who becomes his mentor, Dai begins his journey to master his abilities and confront the forces of evil. Along the way, he is joined by a diverse group of allies, including Popp, a fledgling mage; Maam, a skilled martial artist and healer; and Hyunckel, a former enemy turned ally seeking redemption.

The narrative follows Dai and his companions as they travel across the world, facing increasingly powerful adversaries and uncovering the truth about Dai's heritage as a Dragon Knight. The group battles Hadlar's forces, confronts the machinations of Vearn, and strives to protect humanity from annihilation. The story explores themes of courage, friendship, and the struggle between good and evil, with Dai's growth as a hero serving as the central focus. The series combines action, adventure, and emotional depth, staying true to the spirit of the "Dragon Quest" franchise while delivering a compelling original story.