ok so another thing ive been thinking about with ralsei is. his face. sort of. like everyone has remarked on how he looks like asriel, how his name is an anagram of asriel, and their similarities are even brought up in-game a few times — like when susie comments on kris’ photo of asriel on the fridge and they point out every single difference, and in tenna’s green room when you have the dialogue option to talk about his face, and then further prompts about how you’ve seen it before, think it’s unique or think it’s cute.
if you say you’ve seen his face before, ralsei responds with “Kris, I’m sorry, but this is my face, and if there’s one thing I like about myself, it’s this. So even if you think it’s boring or too similar to [Asriel]…don’t laugh, Kris! If you think it’s the same as [Asriel]…ok, i get it, you don’t think it’s too similar.”
for one thing - i find it really interesting that in both these instances, there’s dialogue from Kris stating that they don’t think he looks like their brother and that he’s actually very different, and with the addition of ralsei’s response, it’s almost subtly drilling it in that ralsei is his own person who only looks like himself.
for another - based on his reaction to Kris saying they’ve seen his face before, ralsei seems to be aware of Asriel in some way, but still insists he doesn’t have a resemblance. and why would that be suspicious? Even Kris agrees, and they’re his sibling. but still…
breaking away from the whole face thing for a moment, we need to reconsider that ralsei is very distinctly not like the other darkners. he knows far more, he’s specifically not tied to an object and his behavior is very different from them in many ways, such as him not really knowing what being “Ralsei like” even means, and his existence seeming to be entirely hinged around the prophecy and meeting Kris and Susie. if he’s hit in battle, he just straight up disappears and leaves his clothes (that he can magically manipulate) on the ground. he can move from dark world to dark world without becoming stone, and there’s also his manual plaque that basically worships the ‘unending pillar of darkness’ that ‘gives [his] body form.’
TLDR: ralsei is made of pure fountain darkness….almost like the roaring knight…. and has an insubstantial form that can be disappeared or manipulated…….almost like the roaring knight……
i also want to tack on the fact that ralsei was so nervous about first impressions he hid his face for all of chapter 1…very not suspicious at all…
SO. my abrupt conclusion to this crack pipe theory is that ralsei made himself look similar (but not identical) to asriel for the sake of befriending Kris, making a “good first impression,” and to better hide whatever else he hasn’t told us.