One day, Lobelia, the daughter of a marquis, realizes that she is the villainess of an 18-rated otome game and that, Lily, her beloved younger sister, is the main character.

"I can't let my precious sister be subjected to such a disgusting situation," she said, "And there's no way I was going to bully her!" So begins Lobelia's struggle to change her destiny!

Before her reincarnation, she had favored the prince's knight escort instead of the prince who was the love interest. As it was a rare opportunity, she was hoping to get the knight escort to fall in love with her while helping her sister. However, the other person is not interested in Lobelia at all. Moreover, the knight escort is crushing every R-event entirely....?

Will Lobelia be able to reach a happy ending?

ある日、侯爵令嬢のロベリアは、自分が18禁乙女ゲームの悪役令嬢であること、そして、愛する妹が主人公のリリーだと気がついた。「大切な妹をいやらしいめに合わせるわけにはいかない！あと、私が妹をイジメるなんてありえない！」そんなわけで、運命を変えるべく、ロベリアの奮闘が始まる！