I recommend the two books,"How Can You Become a Devil If You Don't Cultivate Immortal Cultivators" and "Slaying Heaven and Demon", to you. Both novels are about the protagonist becoming a devil. The former was a story about Xianxia and Qianyuan, which told the story of the female protagonist being forced to become a demon. The latter was a fantasy story about the male protagonist becoming a great demon by cultivating the demon. I hope you like my recommendation. Muah ~