I, the Savior of Mankind, Was Reincarnated into the Seventh Demon King

I was once the last savior of mankind, burning my life to protect civilization. When he opened his eyes again, he became the new seventh demon king in the demon world, and... He was ridiculously weak. The demon body is weak and the magic power is meager. In the eyes of the whole clan, I am regarded as the "shame of the demon king". Until that day, a reward order from the Temple of Light was posted at the door of my castle. It listed in detail the seventeen fatal weaknesses of the demon kings in the past, and invited brave men to come and defeat them. I looked at the very familiar entry and smiled. Every word in this "Comprehensive Weaknesses of the Demon King" was written by me in my previous life. When the first group of brave men rushed into my palace, preparing to harvest this "easy-to-get glory", they saw me on the throne and just raised their hands lazily. "Welcome." I said, "Lecture 1: How to use the classical military formation invented by your ancestors to annihilate a modern squad of brave men." Thus, the most bizarre legend in the history of the demon world began. This demon king does not practice black magic, but specializes in human warfare; he does not build terrifying dungeons, but industrializes the demonic realm; he does not summon abyss demons, but attracts the fourth natural disaster from a group of self-proclaimed "players". When the gods finally noticed this abnormal change and sent down the Judgment Legion, what they saw was the star ring defense line straddling the Demon Realm, as well as the muzzles pointing at their throne, which condensed the dual civilization of technology and magic. This time, I will no longer protect anyone. In the name of the Demon King, I will dismantle this world trapped by gods, and question the being who controls everything behind the scenes: "Are you... Afraid of the "Savior's Weaknesses" written by yourself?"