I will say this about Susan: no one has come close to guessing what is going on yet.
It's not what you think.
There's only so many ways this susan thing can play out. Either she's a real cop(which would make no sense storywise and time wise) or a fake cop.
If we account for her not joining the harem than she loses no matter what and she exits the story. The reason or way it happens doesn't matter much imo because we would already know beforehand she's going to leave in the end if she's not joining.
Now if she is joining or they reconcile then off the top of my head, here are some of my predictions.
1-She's doing all this for attention. MC and her begin having a few rounds of sex. Then it turns into her joining the harem(or part of it) herself with the girls being tolerable of it. This would be so hawt but poor story wise.
2-The MC and Friends stop her from whatever she's planning and maybe she breaks down emotionally with leah personally stepping up and forgiving her. She either still joins the harem after they all reconcile with each other or realize how bad she was and leave again or something.
3- Susan wasn't planning anything at all. Her and MC do nothing and they literally just sit there with her being genuinely hurt by what the MC did to her. It's all heartfelt conversation and a meaningful Apology from MC for what happen. Then Leah and co arrives being bitchy and realize how stupid they were and actually reflect on what they did to her and then all of them group hug it out with a orgy happening immediately after.
I personally see this last one happening seeing as this game like to do emotional moments. If it's none of these above somewhat then I'd be surprised and give a round of applause if it done great. Not going to lie, i went left with this last one towards the end of it though.
These below would never happen because it's either not that kind of game, these girls have strong plot armor or it would piss people off but I'll throw it out there anyway.
1-Susan tricks the MC into meeting and actually kidnaps Leah(or any of the trio) instead to do some Lesbian Dom play.
2-It involves Something with a Uppercase N, a T and ends with R which is never going to happen because of backlash. This may not include any of the harem mind you but more of Susan is the one getting gangbang while the MC is tied to a chair to watch it.
3- She ties the MC up and explores his anal cavity just when the girls arrive and watch. Then they themselves strangely get turned on by it and decides to take turns doing it to him... Dammit those comments above mine threw me off.