In "A Breakthrough Came Out by Forbidden Master and Disciple," Eirth, the son of the hero and the one who defeated the Great Demon King, struggles under the heavy burden of living up to his family's extraordinary reputation. Despite his best efforts, he constantly feels inadequate, hearing remarks like "I can't measure up to my father" and "Never forget you're the hero's child!"
One day, while exploring his father's sword chamber, Eirth encounters the spirit of the Demon King, who offers to train him simply out of boredom. "I'll teach you. I have all the time in the world."
Driven by a desire for revenge against his parents and the world, Eirth undertakes intense training under the Demon King. In time, his parents—the former heroes—his childhood friend and first love, the princess, along with the era's greatest geniuses and the entire realm, will stand in awe of him.