Emi Kobayashi, a young woman who loved an otome game called The Star Maiden and the Knight of Salvation, dies and reincarnates as Remilia, the story's villainess. Determined to avert the ruinous endings that await Remilia, Emi uses her knowledge of the game's events to change the narrative. Over a decade, she befriends the prince and other key characters, solving their personal problems and ensuring a bright future for the body she now inhabits. All the while, the original soul of Remilia remains conscious inside their shared body, silently watching Emi with growing gratitude and affection.

The peace is shattered with the arrival of Pina Blanche, the game's designated heroine. However, Pina is also inhabited by a reincarnated soul, a woman named Rina who is selfish and manipulative. Resenting that Emi has derailed the game's plot, Rina uses underhanded methods, including love potions, to charm Remilia's fiancé, Prince Willard, and the other male leads. Pina then publicly accuses Remilia of bullying, leading to a dramatic condemnation where her engagement is broken and she is exiled. The shock and despair of this betrayal cause the gentle Emi to fall into a comatose state within their mind.

Seeing the woman who saved her from a life of loneliness so cruelly broken, the true Remilia awakens and seizes full control of her body. Where Emi was kind, Remilia is calculating and driven by a singular purpose: revenge. Swearing to utterly destroy Pina and the foolish love interests who abandoned Emi, Remilia crafts an elaborate plan. She will not merely clear her name; she will steal every achievement meant for the heroine, save the world from its prophesied destruction, and become a celebrated hero, leaving Pina with nothing.

The story follows Remilia’s ruthless execution of this revenge. Using Emi’s knowledge of the original game, she preemptively solves the world’s greatest threats, from quelling a demonic invasion to vanquishing powerful gods. She builds a power base among outcasts, including demons, and cultivates a public image of a noble saint, the exact role Pina was meant to play. A key figure in her plan is Anhel, the hidden love interest from the game’s true ending, a powerful and reclusive magus who becomes her ally and eventual romantic partner. While Remilia acts with cold efficiency, she is tempered by Emi's lingering influence, ensuring that while her vengeance is absolute, it brings genuine good to the world. The narrative concludes with Remilia utterly victorious, having reduced Pina to a broken state and forced the remorseful prince and his companions to live with the consequences of their betrayal.