The newly appointed Demon King gazed at the throne beneath him and the lone hero standing before him, then threw up his arms and shouted, "I am invincible!"
But the hero yawned. "I've beaten your ancestor."
The Demon King flew into a rage. "I command a million troops, and none can stand against us!"
"I've beaten your ancestor's ancestor."
"I rule over 17.7 billion people!"
"I've beaten every ancestor in your family tree for eighteen generations!"
"...Can we stop talking about how you beat my ancestors?"
"Fine. I'll beat you now, and still make it home in time for dinner with Xiaoyu."
With that, the hero used a straight punch (magic), the Demon King was defeated, and the world was saved.
In short, this is the story of a former savior hero, busily dashing around the multiverse to clean up all kinds of messes. Don't let the title fool you.