Rachel started out from the simple desire to have a sex negative character at school that would harass the MC and the girls for being too openly sexual. The first, obvious choice for this would have been a hardcore religious type, but I feel like that's been done to death in AVNs at this point. So then my mind went to a review I'd recently read of a light novel, where the professional reviewer was just incredibly toxic and completely unable to tell the difference between a couple depending on each other, and codependency - they literally thought they meant the same thing and that relying on each other is somehow abusive. This reviewer was, of course, a hardcore feminist with a hate boner for the very idea that men and women could actually like each other, and so Rachel was born.