What I'd like to see is the MC being targetted by the NPC sister, either younger or older and being slowly corrupted by their perversion, but not any sissy bullshit.
Along the way the MC/brother needs to watch out for the sister or their mother/father/other siblings might catch wind and blackmail them into something much worse or their parents beat their ass and send them off to military school or something.
The problem is, how do you make the subversion by the sister work. Most people would always choose to allow the MC to be perverted, so what do you do to make it seem natural that the MC would decline without taking the decision completely out of the players hands. I dunno, that's why I don't make games I let other people do it.
