The story follows Cardinal Blauerose, a young girl who believes she has reincarnated as an "evil noblewoman" from a light novel. Having retained memories of her past life as a Japanese office worker who died in a traffic accident due to smartphone distraction, Cardinal finds herself the daughter of the Prime Minister of Menayuha. Her striking appearance, with fiery red twin-tails and sharp cat-like eyes, reinforces her self-perception as an antagonist.
Cardinal's immediate concern is navigating her new life, especially since she lacks experience with otome games, a common trope in her transmigration genre. She has an older brother, Vertimic, who dotes on her, and a younger brother, Yardral, with whom she has a strained relationship, often unintentionally upsetting him. Cardinal's primary motivation is to avoid the typical "evil noblewoman" fate of being disowned and to become self-sufficient, capable of cooking, cleaning, and defending herself. She also wishes to mend her relationship with Yardral and avoid causing trouble for Vertimic.
A turning point occurs when Cardinal, unable to sleep, questions her maid, Ageha, about her and two other staff members, Kagerou and Higurashi, who have distinctly Japanese names. Her astute observation that they might be from a "intelligence division" surprises them. The next day, these three former intelligence operatives reveal their past and, impressed by Cardinal's perceptiveness, pledge their loyalty to her. Cardinal seizes this opportunity to request training in their skills, including illusion magic, hand-to-hand combat, and swordsmanship, alongside domestic skills like cooking and laundry. This marks the beginning of her rigorous training.
Cardinal's relationship with Yardral begins to heal after she apologizes for frightening him with a frog. He expresses his affection, and they bond over reading books, with Cardinal strategically using picture books to improve his opinion of her. Vertimic observes their growing closeness with a fond smile. Cardinal's ambition extends to wanting to be useful to her country, and she discovers that the King's younger brother, Braud, a 16-year-old with black hair and eyes who is excluded from the throne due to tradition, possesses extensive knowledge of medicine. This sparks Cardinal's interest in becoming a pharmacist, believing it will benefit the nation and her family.
Her training intensifies, with Kagerou teaching her illusion magic, Ageha focusing on combat, and Higurashi on swordsmanship. Cardinal proves to be an exceptionally quick learner, even surpassing her teachers' expectations, partly due to her past life knowledge and her innate magical aptitude. She also begins to develop her culinary skills, making hotcakes for her family, which are met with great approval.
Four years later, at the age of 10, Cardinal's engagement to the Prince is announced. This news deeply upsets her father and brother, who are fiercely protective. Cardinal, however, accepts the engagement, seeing it as an opportunity to strengthen her position and influence. During the engagement ceremony, the Prince insults Cardinal's appearance and heritage, leading her to publicly reject him. Her bold declaration shocks everyone, but her father and brother are secretly amused. The King and Queen, however, are impressed by Cardinal's intelligence and character, and the engagement is postponed rather than canceled.
Cardinal then meets the former King, Gardo, and his son, Braud. She expresses her admiration for Braud's pharmaceutical knowledge, and they agree to collaborate on her research, with Cardinal aiming to create items that can nullify aphrodisiacs and charm magic to protect her brothers. Braud, intrigued by Cardinal's dedication and unique perspective, begins to develop feelings for her, experiencing unexplained symptoms of love sickness.
Cardinal's relationship with Braud deepens as they work on their research. She also encounters Braud's mother, Vanessa, a former intelligence operative, who is initially suspicious of Cardinal's intentions regarding Braud but is won over by her charm and culinary skills. Cardinal's interactions with the royal family continue, including a tense encounter with the Prince, whom she scolds for his immaturity and prejudice. She helps him apologize to Vertimic and Braud, demonstrating her diplomatic skills. The Prince, despite his initial rudeness, shows signs of change and even gives Cardinal a hair accessory.
The narrative concludes with Cardinal attending a tea party with the Queen and Braud. The Prince, still somewhat awkward, joins them. Cardinal, recognizing his insecurity, encourages him to apologize to Braud, which he eventually does. The Prince, seemingly developing a crush on Cardinal, proposes marriage, which she rejects, still considering him an "idiot prince." The chapter arc ends with Cardinal having navigated a complex web of political intrigue, personal relationships, and her own developing abilities, solidifying her unique position in this new world.
