The Extra Can't Escape

This is the world of a run-down novel. As the female protagonist's younger sister, I cared for the male protagonist in every way possible to prevent his dark deterioration. Fortunately, he was raised properly, and I thought I'd avoided a bad ending...

"Haena, I want to sleep with you."

So, not with my sister, but with me? I never intended to be the female protagonist!

(Source: Naver Series, translated)

Note: The third story in Daewon's Neungyong Romance Danpyeon (능욕로맨스단편) Collection.