Scattered throughout the world is proof of an advanced prehistoric civilization. There exist those who desperately want to learn more about these ancient people. The series follows people who set out on an adventure to uncover the truth.

Young Dai embarks on an epic journey to become a legendary hero, training with his loyal companions to save the world from the resurrected Demon King.

After the defeat of the demon lord Hadlar all of the monsters were unleashed from his evil will and moved to the island of Delmurin to live in peace. Dai is the only human living on the island. Having been raised by the kindly monster Brass, Dai's dream is to grow up to be a hero. He gets to become one when Hadlar is resurrected and the previous hero, Avan, comes to train Dai to help in the battle. But Hadlar, announcing that he now works for an even more powerful demon lord, comes to kill Avan. To save his students Avan uses a Self-Sacrifice spell to attack, but is unable to defeat Hadlar. When it seems that Dai and Avan's other student Pop are doomed a mark appears on Dai's forehead and he suddenly gains super powers and is able to fend off Hadlar. The two students then go off on a journey to avenge Avan and bring peace back to the world.

Sand Land is a mysterious world where demons and humans eke out an existence in a barren desert wasteland. In hopes of replenishing their water supply, Fiend Prince Beelzebub, a demon named Thief, and a human named Sheriff Rao team up and embark on a journey in search of the Legendary Spring.

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.

The second Dragon Quest Dai no Daibouken movie. The story takes place between episode 18 and 19 of the TV series.

The third Dragon Quest Dai no Daibouken movie. The story takes place between episode 35 and 36 of the TV series. After yet again defeating some of Hadlar's (the leader of the Great Demon King's Army) warriors and saving the princess, Dai and his fellow adventurers are relaxing and helping with rebuilding the island village. Unbeknownst to them Hadlar was usurped by a new demon lord called Galbus, who immediately sets forth to once and for all destroy Dai, using his own sextet of champions. During the initial surprise attack Dai's friend Maam's soul is taken and in order to get it back Dai and his friends must attack Galbus on his chosen batlleground. Will Dai survive this?