Someone asked for the evidence behind transfem ralsei as a theory and not as a headcanon and i put a lot of effort into stuff that i didn't want to go waste in a reddit comment section so here's every piece of transfem ralsei, from minor to major, in chronological order. Welcome to the comprehensive Transfem ralsei guide:
he asks if he looks pretty after wearing a ribbon, the ribbons are supposed to be worn by "the girl" of the story. He blushes after, not taking it off.
if you try to give Ralsei the mannequin he says "the dress looks cute" but refuses to wear a mannequin so he really only likes the dress. The dress that you can see on the mannequin is the same dress that Mettaton wore in undertale, and he's trans. After he wears the dress a lion security guard says "After seeing mettaton in that dress it almost feel like i could wear one too...ha ha ha." and "please don't talk to me I'm feeling discouraged about something." Mettaton seemingly gives them the dress soon after and that security guard is ecstatic. She's known to be a woman in current deltarune. The mannequin that the dress is on appears to be shaped after spamton (shorter addison model with slicked back hair and no palms), who many people theorise could be trans too but i think i talked about the side character so I'll just move on. The fandom calls it "the dress that makes you trans"
after getting the keygen, exiting the roots area and going to Susie and Ralsei, Susie steals Ralseis glasses to tease him and he covers his eyes. He tells her to give it back, but she just calls him a nerd. Then we're shown a sprite of ralsei without his glasses asking for it back again, seemingly serious enough for susie to pump the brakes on teasing him and actually give them back immediately.
you can give Ralsei the "twin ribbon" which is originally noelles as she says it "seems familiar" if you equip to her. Some people theorise Noelle as the "original girl" of the prophecy, since susie, as the girl, doesn't wear ribbons, but that's a whole other thing.
when talking about Kris playing as Susie, he blushes and says "wouldn't that be... confusing". He also seems excited when he has the freedom to be Kris when given the controller and happy he gets the choice to do whatever he wants
When talking about ralseis face he says that his face is the only thing he likes, asserting that they won't put that hat on to cover themselves up again. It's mostly about the hat but their face being the only thing they like about themselves makes with them doing makeup could have a through line if you so interpret it as such.
if you go into ralseis room, the theme "lost girl" plays in his monologue which we haven't seen for any other male character. To be completely fair, this is deltarune and there's way more story relevant girls in the game, so it could just be a coincidence. Either way, it's mainly used for scenes where both Susie and Noelle are lost and trying to parse the world together, so the use of it on Ralsei sticks out.
also confirms ralsei feels constricted by his role in the prophecy, the prince (shocker!). But he seems to call himself princess multiple times. Wearing the princessRBN, being called princess by flowery and being the only princess in the climbing minigame in castletown, etc etc.
castle town climbing minigame, he's the only princess if you don't acquire star walker (but if you do, you can still see him in the dress in the background). He says he's "never tried being a princess before" with a big smile on his face. If you support him, he continues beaming, if you say "nah, bro..." (weirdly toxic masculine way of saying it) he immediately takes it off and talks about experimenting only when it's allowed.
he's repeatedly called a princess by flowery, even though they sometimes intentionally avoid calling Kris a princess.
in the sauna scene their glasses fog up, they take them off and put them to the side, revealing what seems to be eyeshadow in their talk sprite. They make an excuse of water getting in their eye and wipe off the makeup then go back to their glasses that were just fogged up and put them back on just to continue talking. It's a really odd sequence that's not acknowledged, only existing to emphasise that Ralsei took his makeup off for no reason. (sprites for example)
after the orange and green fight flowery will have a heart to heart with Ralsei, offering a "pink and blue" coupon that they have been "looking at the longest". Pink and blue, trans flag, blah. People think this is about Kris and Susie but this was mostly on a scene where Ralsei was told to not care about Kris and do something for themselves, so i doubt it. (Also pink is never mentioned as a kris colour and susie is exclusive referred to as purple. Blah blah blah)
before leaving, Flowery calls Ralsei a princess and boops his nose. Ralsei blushes and does not respond Flowery leaves.
the game gives you an option to close your eyes and imagine Ralsei in the scene where the previous two points happen. If you choose to say no, the game gives you another option "Close your eyes and think about Ralsei / Don't even though it seems really really important" The last time the game emphasized how a scene could be important to watch and advises you not to skip it is the suselle Ferris Wheel sequence back in chapter 2. And that was REALLY big set up for one of the most important relationships we have now. Despite that, we have no idea where this set up is taking us. The game gives you an option to take the blue and pink coupon from Ralsei, but it's not a real option. If you pick the voucher Ralsei wants, Susie will stop you and say that's the one Ralsei clearly wants, they then blush and get happy that their friends have them in mind. If you pick the other one, Ralsei gives it to you and gets happy that Kris has them in mind anyway.
after you finish both flower sequences and climb the vine, Ralsei title changes to "artemisia" which is a flower family named after a female god of nature that was surrounded by other women (idc for greek mythology sorry). It's also the first time the game uses they/them for Ralsei.
when talking to asgore about Ralsei he says "I hope that they learn that they don't have to hide themselves" (Note: use of they on Ralsei. Asgore uses exclusively they/them for ralsei as well iirc.)
Ralsei says that flowery is pretending to be something he's not, flowery lifts their chin to look eye to eye and asks "and would you tell me what's wrong with that?" all smug and Ralsei doesn't respond (paraphrased, same idea. U get it)
And that's it. There's also the general idea that Ralsei doesn't like his role in the prophecy, which is an allegory for cagey societal roles, and his role is inherently a masculine one. A lot of it happens in chapter 5, which is where a lot of gender stuff gets mentioned (Rudy mentions two queens winning for the first time in the king and queen thing, implying general hetero normative society in hometown, Noelle saying that in their childhoods they didn't know who between her and Kris would be the king and queen, meaning they never really had a non gendered role for Kris. The secret boss being a transfem character from undertale. Seth...just seth, being the ralsei of the flower squad, just not knowing what their gender is. And green, being another non-binary character referred to with they/them.
Either way, this is just a theory, and a lot of it could be just chalked up to reading too much into stuff. And talking about reading stuff, i am not proofreading this. If there's a typo or grammatical inaccuracy, i am not checking. U gotta figure it out urself I'm too tired.
