Sai Ren Na De Dingzhi Rensheng

Medea, the witch novelist, was about to die from staying up late writing too often. Before her death, she specially tailored a novel for herself, intending to transmigrate into the book to live a perfectly scripted life. But — her perfect loving prince became a perverted killer; her loyal knight became a misogynistic homosexual; and her doting older brother became the villain's lapdog. She was supposed to be the perfect heroine, but she became the evil villainess instead! In order to survive, Medea had to marry… no, form an alliance… with the despised Demon Lord!

(Source: Tencent, translated)