The way to defeat the Archfiend / 打倒魔王的方法

Once upon a time, there was an unbeatable monster in the devildom. He was so invulnerable that nothing can hurt him, and being enchanted by magic could not be more serious than being bitten by a mosquito for him. Over time, both the human and the monster were so afraid of him that he got the title of the Archfiend. However, being invincible was so lonely. Though he was a world-beater, he had no friends around him, let alone a girlfriend. Finally, he was provoked by the Brave couple with displays of affection. Then he decided to venture around the world to find his companions and set up the leg...