After transmigrating to another world and becoming the Demon King, he returns to Earth. He conquers the people of Earth and makes them join him in resisting the monsters from the other world. The protagonist is no perfect hero. He's an idiot who can't keep his mouth shut, with a charm score of just 1, meaning that out of every hundred people, only one will become his friend or follower. He can only force humanity to defeat the monsters and save themselves through the Demon King's brutal rule. That's why he's called the Demon King.
