After Becoming the Guardian of a Mortal Enemy

[The Crazy and Evil Demon King Shou——Moral pacesetter (but with double standards) is the main savior] The Demon King was improperly sealed for tens of thousands of years. Once he woke up, human society has entered the era of super technology. Bad news: Seal it for too long, and the Demon King loses his arrogant power. Good news: His nemesis, the savior who can fight evil spirits, can only be possessed by a four-year-old human cub! If the devil was not careful, he could have been crushed to death with one hand, but unfortunately, fate has its way with the devil. ... He was forced to become the guardian of his mortal enemy. It carries a powerful will from ancient times, but it is a mortal body. It must have three meals a day, the air conditioner cannot be too high when sleeping, and the food must be eaten by children. It even gets sick and needs to be given medicine! ———— This is a centralized civilization where the world has achieved great unification. A society governed by law is based on science and technology. There are no monsters and ghosts, and there is no need to fear the so-called gods and demons. However, the rulers of the hyper-technical era also seem to come from ancient times. How did the world go from the chaos of demons to the civilized era? Why is there an unfinished contract in a timeline where the Demon King has never appeared? How could the true form of the sworn enemy be left behind in the old civilization in history? In order to make up for the old covenant, the Great Demon King descended to Huidian to find his true identity. The guardian and the ward went back in time and traced the past to reveal the truth layer by layer. This is a ridiculous collision between a lost old world and material civilization~ ——The truth is, don't believe the truth. [The arrogant and arrogant demon king who catches someone without realizing it is indifferent on the surface but secretly suppresses the attacks from his inner demons] [Tips: plot line 67%, emotional line 33%] Intention: Constantly strive for self-improvement!