Oshi no Imouto ni Tensei shite Shimatta node, Saikyou no Akujo ni natte Onii-sama wo Dokusen suru koto ni Itashimasu

Amamiya Nagisa harbored an intense devotion for Neun, the wicked marquis from her favorite light novel. When she found herself on the brink of death, she expected to fade into nothingness. Instead, she awakened in the very world of that story, reborn as Frau, the younger sister of the man she adored. Although they share no blood ties, a romantic relationship between siblings is considered a profound taboo within the society of the novel. Despite this societal barrier, Nagisa refuses to let go of her feelings. The mere thought of another woman capturing Neun’s heart fills her with unbearable jealousy. Determined to keep him entirely for herself, she resolves to fully embrace her new identity as the infamous villainess Frau. Armed with her knowledge of the original story, she sets out to systematically dismantle every romantic opportunity destined for her brother. By destroying all his potential love interests, she intends to ensure that she alone stands by his side, claiming the evil marquis's affection through sheer force of will and cunning.