War between humans and demons is the backdrop for the story. The Humans' greatest hero storms into the castle of the Demon Queen and vows to defeat her. Rather than retaliate, the Queen offers to form an alliance with the Hero. When the war is over, she continues, the Humans will begin fighting among themselves, just like they currently do in the Demon Realm, and this could lead to even more turmoil in the planet. He unites with her in order to bring prosperity and peace to both humans and demons alike, convinced by her claims.