Gaiaku Ane to Ketsubetsu shimasu

Clara had been oppressed for many years by her tyrant sister, Enefia. Even their parents obeyed the sister's wishes, and Clara had no place in the Baron Astraia's household despite it being her home. In the midst of this, Clara's sister's engagement to a prominent nobleman was decided, and Clara finally felt relieved, believing she would be freed from this hell. However, even after the engagement, the sister's unfaithful nature did not change, and fearing the fiancé might discover the inconvenient truth, the parents ordered Clara to monitor her sister. Despite Clara's efforts, her sister became pregnant with another man's child. The engagement was broken off, and the sister quickly eloped somewhere, leaving the Astraia household with a huge debt and angering the influential nobleman. In order to repay her family's debts, Clara was sold to a sadistic noble and faced severe torture, ultimately approaching death. "If I could do it over again... This time, I will definitely kill you!" When Clara opened her eyes again, time had rewound to the day of her sister's engagement. Revived with strong determination, Clara pushed back against her sister's insidious bullying and ran to change the worst possible future. (Source: Shueisha, translated)