Mistake! He’s not the male lead, he’s a psycho demon.

Ji Xueli transmigrates into a novel as the female supporting character who serves as the male lead's white moonlight. She enters the story without knowing the novel's title or the male lead's identity. The system bound to her, known as the Female Supporting Character System, is malfunctioning due to data corruption and cannot identify the male lead. Ji Xueli is the only daughter of the Ji family, one of the four great aristocratic families in Huacheng. In the original plot, she abandoned the male lead when he loved her most, then left for Germany. The male lead subsequently meets the female lead, a resilient woman from a poor background, and their romance becomes the central storyline. Ji Xueli's task is to climb the ranks and alter her fate, but she must first locate the male lead.

At a monthly maritime ball, Ji Xueli spots a man named Duan Qingyu, who exudes an imperial aura. The system identifies him as the male lead based on his appearance and status. Duan Qingyu is the leader of the Duan family, the most powerful clan in Huacheng, and the head of START Entertainment. Ji Xueli approaches him, and he reveals that he remembers her from childhood. Their interaction is tense, as Duan Qingyu harbors resentment toward her for leaving him years ago. Cheng Du, a mutual acquaintance, informs Duan Qingyu that Ji Xueli wants to pursue him. Duan Qingyu agrees to let her try, viewing it as a game. He tests her by asking if she wants him included in her pursuits, and she responds with boldness, which intrigues him.

Ji Xueli returns home and learns that her parents plan a dinner with the Yan family, implying a reunion with Ji Yanzhou, the original host's ex-boyfriend. Meanwhile, Ji Yanzhou receives news of Ji Xueli's return and is disturbed by it. He encounters Xie Yujun, his assistant, who has feelings for him. Ji Yanzhou remains emotionally distant but protective. Ji Xueli goes shopping and encounters Ren Tang, an actress who claims to be Duan Qingyu's mistress. Ren Tang tries to humiliate Ji Xueli by snatching a limited-edition bag, but Ji Xueli slaps her. Duan Qingyu arrives and dismisses Ren Tang, revealing he has no interest in her. He then invites Ji Xueli to dinner, and they are joined by Ji Yanzhou. The dinner is awkward, with Ji Yanzhou coldly ignoring Ji Xueli, who remains indifferent in return.

After the dinner, Ji Yanzhou rushes to the hospital because Xie Yujun was attacked. Ji Xueli accompanies him, showing no jealousy. Cheng Du picks up Ji Xueli and mentions seeing Ji Yanzhou with Xie Yujun. Duan Qingyu listens to the conversation and becomes more interested in Ji Xueli's true intentions. Ji Xueli attends a club gathering with Duan Qingyu and Cheng Du. Duan Qingyu proposes a condition for her to join START Entertainment: he wants her. Ji Xueli accepts the condition, surprising him. She drives them home recklessly, and at his residence, she demands top resources and the firing of Ren Tang. Duan Qingyu agrees to her terms. She then claims that during her three years abroad, she only thought of him. Duan Qingyu is visibly affected by her words, though he remains outwardly cold. The story continues with Ji Xueli navigating her new role in the entertainment industry while managing her complex relationship with Duan Qingyu and the lingering presence of Ji Yanzhou.