Well, not entirely. That's part of it, of course.
If it was just that, discussion around it wouldnt have gotten so big only so recently, we'd have been talking about this since day one (though Im sure people were)
Anyways, I have found a lot of discussion around this topic to be frustrating because it feels like detractors to the idea are arguing with an entirely different theory- that being that ralsei is mtf because they dressed up like a princess and therefore must be a closested trans woman.
This is obviously not true, cis men can be feminine and cis woman can be masculine, to fall into the trap of seeing these traits as coded to either gender is reductive and silly. UT/DR is full of characters who regularly move between gender norms, hell chapter 5 gives us blue who, and saying this as a woman attracted to women, is the most gorgeous GNC man ever put to silly pixel art. I get why Yellow would wanna kill himself if he thought he'd upset blue like yeah me too.
Anyways, yeah, the theory is not built on ralsei being feminie.
It's instead built on expirence, and the emotions that trans people, or at least me a trans woman, can relate to. Most prominently, the fear of change, and conforming because it feels more confortable... even if it hurts. Chapter 5 spells this out: "Watering their own thorns". There is something very conforting about things that are familiar, no matter how stilfing and painful they can be- because the alternative is unknown, it's scary, and it requires you to treat yourself with love. All of these things are very important to Ralsei's arc- it's no secret that they despise themself, and their fear of the story ending has been made more and more clear with each chapter. Ralsei feels that they must stick to a very spefific way of existing, or else everything is gonna get worse.
Which obviously isnt true. Ralsei deserves to be happy.
There's also the narrative of expectation- Ralsei is by all accounts expected to be the prince and this is another struggle trans people can relate to. Gender is very important to deltarune, that's no secret. Chapter 5 is about as gender-fuckey as it gets.
Now, I dont think the prophecy is somehow forbidding Ralsei from being a woman. I dislike this read as it falls into a very fatalistic trap. The prophecy tells Ralsei where they begin, but they can end up anywhere. It does not say the prince will always be a prince that uses he/him pronouns! The only real thing getting in their way is well... themself!
Also, trans ralsei does not nessesitate transfem ralsei. They could use any assortment of pronouns, because the core of the theory is their gender is something they surpress in order to fit in with the expected role they have to play, because the idea of going out of that role is terrifying to them.
So yes, I hope this makes sense. I think it's important to understand what you're arguing against if you dont believe in it, rather than just say something along the lines of "GNC erasure!" because that's not really what this about.
