In "Shera and the three treasures" you play the hero's younger sister on a quest to save her brother and the world.
You don't really see a whole lot of the brother, and for the game he's pretty much irrelevant (no naughty sibling stuff going on here), except that introducing her as the sister puts you in a place where you actually want to protect her and her innocence (at least it was like that for me - but then again, I am an older brother...).
Since dialiogue choices and battles both pose a threat to her virginity, you are basically on edge throughout the entire game, most of the time you can read the mood in critical situations.
You can definitely succeed but especially to new players it will be a real challenge. The game can be completed without all that though and you can go around accumulating "mileage" from all the enemies and monsters, but for me that would kill the thrill
I found that the game - although skipping through some dialogues could be faster - has replay value when you put handicaps in place like "no buying items" or "no repairing clothing" or even "no saving/loading" and so on.