The story begins with Cordelia Hamilton, the daughter of a Duke and a high-ranking official in the Ad Astra Kingdom, experiencing a sudden influx of memories from her past life as a Japanese high school student. She realizes she has been reincarnated as Cordelia, the villainess of the otome game "Etoile of the Magic Academy," and the girl brought before her, Stella Oakwood, is the game's protagonist. In the game, Cordelia is destined to torment Stella and ultimately face ruin.
Overwhelmed, Cordelia, now possessing her past life's knowledge, intervenes when Stella's entourage attempts to douse her with water, a scene she remembers as a trigger for Stella to gain favor with Prince Alphard. To prevent this, Cordelia claims to have called Stella to confess her love, shocking her entourage. To her surprise, Stella reciprocates, accepting Cordelia's confession. This unexpected turn leads Cordelia to embrace a "fake yuri" life to avoid her destined downfall.
A week later, Cordelia and Stella are inseparable, attending classes together, sharing meals, and studying in the library. Cordelia's past life personality and knowledge blend with Cordelia's existing habits, leading to more nuanced behavior. Stella is shown to be an avid reader, particularly of romance novels, which Cordelia confiscates, only to later find them surprisingly tame.
A month passes, and their relationship is now common knowledge. Their peers observe their closeness with amusement, noting Cordelia's softened demeanor. Stella, a skilled cook, prepares lunch for Cordelia in the courtyard. Their peaceful moment is interrupted by Prince Alphard and his elite friends, who question Cordelia's sudden affection for Stella, suspecting ulterior motives. Cordelia, feigning remorse for her past behavior and professing genuine love for Stella, manages to convince them of her sincerity. The prince and his companions, witnessing their bond, declare themselves protectors of their relationship, forming the "Magic Academy's BIG-4" and vowing to intervene if anyone tries to disrupt their union. This unexpected development solidifies Cordelia's avoidance of her villainous fate but leaves her with guilt for altering Stella's destined path.
Determined to ensure Stella's happiness, Cordelia decides to focus on securing financial independence and social standing for both of them. She encourages Stella to pursue her dream of becoming a magic tool craftsman, a growing field. Cordelia resolves to do the same, aiming to build a secure future for them. They begin studying diligently, with both excelling in their exams.
Cordelia attempts to cook for Stella, but her lack of experience with traditional cooking methods results in burnt food. This inspires her to invent a "magic stove" by adapting the existing "magic heater" used for baths. She enlists Stella's help, and they begin research at Cordelia's family estate during the summer break. Their parents, initially hesitant about Stella's presence, quickly agree after receiving a letter from Prince Alphard.
During their research, they face challenges but also find moments of connection, including a swimming lesson where their closeness becomes palpable. After numerous prototypes, they successfully create a functional magic stove. They decide to patent their invention as the "C&S Workshop," ensuring its exclusivity.
As they prepare to present their invention and return to school, Cordelia confesses her past-life knowledge and her guilt for manipulating Stella's fate. She offers to end their relationship and give Stella her entire fortune as compensation. However, Stella reciprocates Cordelia's feelings, revealing her genuine affection and desire to continue their relationship. They share their first kiss, solidifying their bond.
Returning to the academy, their relationship continues to deepen. They now share intimate moments, occasionally staying overnight in each other's rooms. Cordelia reflects on how her initial deception has led to an unexpectedly happy future, with her and Stella walking hand-in-hand towards a shared destiny.
