Fantasy novel, the protagonist is forced into a demon! Those who are driven into demons by the right path, those who hate them, and those who degenerate into demons will do!

Ding Xiao is famous for killing immortals. He was forced into a demon in the early stage and returned to normal after revenge. Later, he became a demon in the land of demon spirits (not a demon, but he killed thousands of people and was too angry), and then he became a demon in the civil war. . . . . It's a good book anyway. Look at other answers, also written by ears, mainly because the middle part is enchanted, mainly because of the mystery of my body, the betrayal of some people and other similar problems of bald cranes. But it may not be as magical as you think.