Well, how do I want the main game to be?
Simple question, not so simple answer.
1. Main character
On that I'm open to suggestions. I even started a poll.
Most people would like to play Ruby or other RWBY members.
I'd like to do that, too. But it could get partially in conflict with other aspects.
2. Gameplay
In comparison with the trailer: Less, less fighting. Instead focus on character interactions - whoever is MC (or MCs).
On how to work out corruption: Let's say "subtle". I stated that only playing Ruby could end up in your typical RPG, where you "accidentially" be transformed into a slut. i do NOT want that. Subtle means: Slow corruption. In the best case, there is an antagonist, who you don't have to play. But you could show him/her and make clear, that he/her pulls the strings.
That could be Ozpin, Torchwick, Cinder (Salem), a random student like you suggested or even Yang.
Than there are several things - let's say weakpoints - that these antagonist could use on Ruby to corrupt her. (Responsibility as a leader, bond to friends, dependency on crescent rose, her shyness (social awkwardness), her love for battle skirts or her blossoming love for Weiss, etc.
Additionally we can adapt the outside world to be more sexual in general. But this I would place in...
3. Storytelling
To make one thing clear: THAT is what I wanted to focus on. Since my programming skills are just starting to grow and my artist skills are quite simple, here I already invested most of my thoughts.
To me there are 2 options:
A: Make one compact game like your standard RPG. Ruby becomes a slut. FIN.
B: Make it big. Like REALLY big. Make a game for every season. Adapt the story and lore just slightly to your benefit. Make it complex and beautiful. Overcome even the narrative of the original. (after Monty's death :/ )
As you might already can see: I prefer option B.
In my 1st thread-reply I named a lot of possible directions, that a different MC, gameplay and storytelling could lead to. I don't know if you are familar with them.
But option B here comes close to "The Last Sovereign". It's H-scenes are text only but the complexity of the world, the charaters, the story and the possible decisions make more than up for it.
Since I also can't offer much (original) content for H-scenes and scenarios like "Akabur's witch trainer" or "HentaiHighSchool" wouldn't focus enough on team RWBY, I'm more and more in favor with this option.
4. End goal
If you go with option B, three more options here:
B1: Make the corruption really subtle. Fully corrupted Ruby at the end of everything. Con: This doesn't leave much content for the early game.
B2: Game 1: Corruption of Ruby. Game 2: Corruption of Weiss. And so on. Different order possible. Con: Difficult to achieve storytelling-wise.
B3: Harem-route. Kinda like TLS. The harem members are becoming more and more open to sexual stuff, but their personality stays intact. No "from saint to cock whore in 10 minutes". Con: Every harem needs a leader. I see noone perfect for that. Best might even be a random male MC (Jaune maybe?). Second option would be: Ruby, Yang, Cinder, Oscar, random female.
Again, I'm in favor with the last option. Ultimate pro argument would be: The final consequences of the player's choices could be who ends up as a couple. So the Bumblebee, the White Rose or even the Jaune-Pyrrha shippers could get their happy ending.
I also personally dislike seeing Ruby as a mindless cock whore. So in the end she might be even able to save the world. But to get there she has to "mature".