What's Wrong with a Hero's Second Life as the Demon King's Disciple?

For his mediocre performance, Les Field was called "Useless the Second" and "the Hero's Mediocre Son."

Living with resentment and in the shadow of his forebears, he encountered the spirit of a Demon King who had been dead for twenty years in a secret room in his family home.

"Boy, I have a grudge against your father..."

"So... let me teach you how to defeat the person you think you can never surpass."

And so, the former Demon King became the son of his enemy's mentor.

The mediocre second generation of the "Seven Heroes" set out on his journey.