I Became the Demon Lord and my Territory is an Uninhabited Island

Our protagonist Caam is a man from Earth that was reincarnated into this world as a demon. In order to survive, he spared no effort in avoiding the sparks of battle and without noticing it, he became strong himself. Then, one day a demon that is stronger than himself suddenly appeared in front of his eyes. The demon said 「You seem quite strong. Don’t you think someone that strong should become a Demon Lord?」. He tried to negotiate but he had no right to refuse.