Call Me His Majesty, the Demon Emperor

My name is Wang Bu'er. I was an ambitious young man who led monkeys around the park, until a beautiful woman told me I was the strongest savior in a thousand years, and that my monkey was the Great Sage, Sun Wukong. You think this is a clichéd story about a good-for-nothing saving the world? No! When heaven and earth crumble and monsters return, Wang Bu'er is terrified when he comes face-to-face with the legendary Taotie. But then the divine beast suddenly kneels and calls him Lord Demon Emperor...

So Wang Bu'er has to defeat the Demon Emperor as the strongest savior, while also defeating the savior as the Demon Emperor reborn.

Wang Bu'er: ??? I defeated myself?