Saa, Akuyaku Reijou no Oshigoto wo Hajimemashou: Moto Shomin no Watashi ga Idomu Zunousen

Would you become the villainess to save your beloved baby sister? That was the deal promised to Mio Satou by Shizuki Sakurazaka, heiress of the Sakurazaka Group, one of the most powerful conglomerates that dominate modern day Japan. The terms? Take her place in life. Survive three years at an elite academy where the progeny of tycoons and moguls roam, and in return, Shizuki will cure Mio's terminally ill sister. But in a revelation that turns Mio's world upside down, Shizuki reveals that their reality is based on an otome game from her previous life, with herself as the game's original antagonist—an antagonist whose downfall was essential in guiding the world to its happy ending. Now, as former "commoner" Mio steps into the labyrinth of high society, can she successfully navigate her way to her predetermined demise and her sister's rescue, or does more than just doom await her at the end of this journey?

(Source: Cross Infinite World)