I Work Undercover in the Demon World

Tang Chuan, a dissolute immortal, is required by the Immortal Emperor to work undercover in the Demon Realm. From then on, he's fitted in there like a fish to water. Surrounded by various gorgeous girls, he gets promoted again and again. Three years later, Tang Chuan says to the Immortal Emperor, "If you still don't close the net, I'll become the Demon King." (Source: Webnovel)