You would have to wait for the sequel, sorry... chaderin is real...
You have to keep in mind that most content in this arc is optional. It's possible to do only the Sera stuff and move the story along.
The Erin femdom stuff isn't necessary at all, and it's for those people that enjoy that kind of thing.
The gender bender option will occur when starting the next and final story arc. That's the normal progression.
Mars chooses Sera or Ceci, then later in the 3rd arc the option to gender bend Erin is introduced.
The femdom route is an alternate route to get there.
I think I said this before but NPC content doesn't make sense for Mars to do, it's just there because the player wants to do it. In the original spec document it was even more explicit than that with the bad end requiring corrupting the NPCs but I changed it in the end.
The NPCs are there to cover a situation/kink for variety's sake, it's up to the player to decide if they want to bother with each one. All of it optional for the story.
Let's think about it another way, if I were to reduce all optional stuff and try to adapt it into a linear story.
I would have Mars going from Ceci to Sera and probably end with Sera. Ignoring the temptation of NPCs and Elena as that stuff is illogical for Mars to do.
Hope this makes sense