SHE IS A VILLAINESS IN AN AGE-RESTRICTED OTOME GAME, BUT HER STAUNCH KNIGHT IS TOO GOOD TO CAUSE ANY R-RATED EVENTS

Suddenly one day, the marquess's daughter Lobelia realizes that she's inside the world of "The Eternal Cage," an adult dating sim she played in her previous life. What's more is that she's the villain of the story, while her dear sister Lily is the protagonist! However, "this time," Lobelia vows not to bully but protect her sister, especially from any "compromising circumstances." Thus begins Lobelia's struggle against fate, and the beautiful yet lusty men it throws her and her sister's way! (Source: MangaPlaza) — Description from AniList community (anilist.co).