I mean I do really like the idea of a more comedic start, especially since I think in the setting it could work,
especially if it's, as you say, born from mutual attraction. The protagonist kinda wants to get her to retaliate (read as: being dominated/disciplined by her + also genuinely thinks it would help her overcome her insecurity and "just be quiet and take it" attitude towards mean people) and is more being a brat and kinda-tsundere type character.
The fact they both come from different social classes makes it really hard for Rue to place the behavior, is it just the usual bullying of an uptight upper-class person
and towards a Futa (honestly I feel like it would be more unusual for someone who appears to be a loner and had some pretty unkind experiences in her past to be able to easily understand that the protag has no ill intentions)?
That combined with flirty or maybe even sometimes raunchy flirting would probably have her on the edge, understandably, so it seems like things could escalate to the point where the game starts even without really malicious intend on either side.
In my humble opinion it would quite make sense for Rue to be clueless how to approach the protagonist after realizing what her curse did + that she can't undo it. The protagonist being bad at openly communicating their feelings would probably be a sound reason for them to think they fucked up and made Rue feel so terrible about herself that she felt the need to disappear (maybe they even worry she did something to herself) so they kinda wanna disappear themselves and leave behind their luxurious life as a form of self-punishment. You could even leave in the pretty harsh scene at the end of current content as maybe a dream the protagonist has (with some adjustments to the dialogue ofc to reflect the changed premise) because subconsciously they wish Rue would do that to them, punishing them, instead of whatever she supposedly did to herself.
In my mind perhaps Rue would be aware of that dream occurring because their feelings for each other + the magic she used created a bond between them, but obviously it would again be something she'd probably not immediately know how to interpret.
This is me laying out the concrete idea that formed in my head while now really thinking about it, but that doesn't mean I think you should implement it that way. Just in case some parts of it resonate with your own creative energy again I thought it could be worth writing down. Also I just like musing about games I'm intrigued by and coming up with what I feel like are at least not entirely outlandish ideas.
I will say though I don't want to give you the feeling you need to do extensive rewrites so, once again, don't think your current story is not at least as good as this alternative. From my experience a lot of people really enjoy darker stories & even though I do not so far I got the impression that even with the current premise you don't plan to make this all misery but instead there is 1st of all the option for the protagonist to become a much better person & also make things up to Rue (even though it seems clear she's going to be cruel and abusive for the time being, for relatable reasons) and 2ndly there are also characters (or at least 1 character for certain) like Violet, who at least so far seems to lean towards a far more wholesome relationship right from the get-go.
I am not entirely sure how a start that is centered around Rue & the Protag actually having feelings + the hots for each other leans itself to romantic interactions with other characters, though. Obviously a good portion of it (the sex part) can be justified by the curse making it so the Protag
has to find a source of sustenance, and Rue hiding at the start definitely would tie in well with that in my opinion, but obviously in the long run it would not be entirely easy to write under this premise without broken hearts which would kinda counter the idea of making the story itself more wholesome and lovey-dovey. I'm not sure if it would be a satisfying solution to say Rue just doesn't mind sharing the protagonist from an in-story perspective, unless it is specifically something she enjoys. Also there is ofc the chance you intend for this to be a harem-kinda game where the protagonist gets to freely romance multiple NPCs, which I ofc wouldn't know about since I thankfully can't read minds. :'D
There's ofc also the factor that it would probably better if the player isn't forced to play as a protag who wants multiple partners, let alone sharing their SO (or even multiple, this is a game after all, so it should be okay to be a bit unrealistic and not force this sorta dynamic to go both ways).
Edit: Can't help it, still trying to come up with immersive ways to keep things in the general course the game already is on: What if Rue basically watches the protagonist unbeknownst to the latter, seeing how they (as an example because she's the first NPC of that sort) develop the relationship with Violet, seeing that the protag apparently doesn't hate Futas (if the approach to Violet is opening up to her, not simply going down on her to satiate the thirst), once that becomes a general theme in how the protag goes about their way of treating the Futas they meet Rue over time gathers enough confidence to approach them since they aren't confined by the surroundings of their old lives anymore so that finally they can be open about their general thoughts and feelings, but especially their feelings for one another?
Also I thought the protag could perhaps not even know about the curse initially and think that they are being punished by some higher force for what they did (I assume the part where the protag reveals Rue's secret wouldn't be a thing with that start anymore, but they still were teasing/bullying her and also closeted about their disagreement with how the world treats Futas and that they didn't consider Rue as beeing beneath them but instead were insecure themselves) so while maybe initially hesitent to "betray" their feelings for Rue by getting it on with e.g. Violet they'd realize they have to somehow get their fill of sustenance, but also after some time decide that they can only make up for their wrongdoings by starting to openly treat any Futa they meet with kindness and consideration, maybe even developing the guts to speak out against their mistreatment, in time. At the same time Rue, from their shared dreams, comes to understand what the protag's motivations were on top of seeing they never felt ill about her being a Futa.
Well, you can probably tell I'm pretty invested in your game. I'm sorry for gnawing your ear off
Oh, yeah, I mean Rue is very unkind and normally her act would be beyond what I really can accept before starting to dislike a character & definitely not wanting romantic interactions with them, but what the player character did is
so messed up, vile and cruel that I can't condemn her. Especially given that it went for a really long time & she literally didn't do anything bad to the protagonist prior to the escalation we get in the game. So you 100% succeeded at what you tried to do. At the start of the game I really didn't like her, at the end I really didn't like the person the protag used to be. XD
Final note: I absolutely agree that the whole gameworld should stay the exact same. Not only does it literally make the comedic start far more believable and logical, because it creates a setting in which this kinda harmless teasing becomes super easy to mistake for something darker, but it also means the 2 main characters Rue + PC could very well struggle to find a way to openly communicate before it's too late (and the curse happens) and that then translates into them running away from the confrontation and especially openly facing their potential misbehavior. The whole thing being set in the gloomy world you already created with the truly dark start we have right now also makes the wholesome moments and especially the development of Rue's and the protagonists relationship into the happy-end lovestory Rue (in my personal opinion) deserves (I mean no matter the protag they can start a family in the long run) all the more satisfying and heartwarming. Personally I'd think it would make sense if it is a relatively clearly defined dom/sub relationship still, so you could easily stick with Rue getting more and more bold with her "payback" (once they've met again and she probably understands the antics of the protagonist better and better) but ofc it's entirely up to your vision and choice, I just interpreted the things that happened so far as Rue intending to dominate the PC.