You have Eternum as your number 2 game, every LI in that game, except the milf, is a virgin. The only difference between virgin characters and a non-virgin characters is how a dev chooses to write them. If virgins are shoehorned into only a few stereotypes, that isn't because those are the only ways a virgin can be written, it's because most devs are not very good writers.
As for this game in particular, I simply have no interest in a sloppy seconds sister, it destroys the intimacy which forms the core of that relationship. There's nothing special about fucking your childhood friend, sister, daughter, girl next door, high school crush, etc... if everyone gets a turn, especially when the main antagonist is the one who fucked her.