I, the Strongest Demon, Have Regained My Youth?!

Xin Sheng, an unrelenting demon ruler who once controlled the world, ventures deep into the domain of evil spirits in search of the highest and lowest levels of power. He does so to keep up his standard. Millennia later, Xin Sheng has become both stronger and younger, while the world around him has changed. The story follows him as he faces this transformed world.