After I Entered a Torment-the-Protagonist Novel, I Stole the Boss's Script

Si Xuan transmigrated into a novel where the protagonist was put through endless torment. In the original story, the heroine's family was destroyed when she was young because people coveted a secret treasure left behind by her ancestors. After joining an immortal sect, her unusual constitution led everyone to treat her as a cultivation vessel and cast her into the abyss. Until just before the ending, the heroine was tormented over and over in every way imaginable. Si Xuan was left with a head full of questions. Now she had taken the heroine's place and was standing before the ruins of her home, which had just been burned down. The villain had arrived too late to do anything but set fire to her house. He smugly told her, "If you want revenge, come find me at Wuwang Peak! Hahahahahahaha!" Then he swaggered off. Si Xuan: To hell with the original plot. I'll turn evil right here and now, join the enemy, and take the final boss's role while I'm at it. A few years later... Si Xuan, a black demonic mark still printed at the corner of her eye, sat in the guest chair on Wuwang Peak. She greeted the little villain from back then with a half-smile. "Hey, we're colleagues now." The little villain: "..." The Demon Lord, who had lost most of his scenes to her: "...Why don't you think about taking me, too?" The title and blurb may be changed. Theme: Never give up.