As of now, there's nothing about Ralsei's characterization that's in conflict with what I expect of him — that is to say, I'm not disappointed or confused by any of it, as a person imbibing a story. He doesn't feel incongruous with the rest of the story or characters being told. And I currently, very firmly see Ralsei as Asriel, so I don't feel like there's anything about him that doesn't mesh with that reality. To me, the things we cannot fully explain yet feel fully intentional; it's part of the mystery of the game, that we're steadily uncovering. We've only just hit past the half-way point 'til the end of the game. There's so much left to uncover... and I'm eager in anticipation to learn more.

That being said, I feel like there's enough information presently available in DELTARUNE and UNDERTALE both to conclude this, if one is attentive and invested enough. I've been confident that Ralsei is Asriel since Chapter 1, and nothing has caused my stance to waiver since then. To me, it's not a matter of 'whether or not Ralsei is Asriel' but more of a matter of 'Why is Asriel presenting himself this way? What is his goal?' And more recently, I've started to wonder, 'What magic is at play here?' Initially, I was certain that Asriel was roleplaying as Ralsei, Prince of the Dark this entire time, but as Chapter 3+4 introduces entities like The Roaring Knight and Gerson, I'm less sure about the... mmh, composition...? Of Ralsei. Whether or not he is some sort of altered state or artificial creation is yet to be seen, for me. Kris very much seems to be tampering with their own level of awareness/memories (the separation of SOUL and SELF...?) As Ralsei reports, the Dark World can can create darkners 'patterned after the memory of a loved one', so it's possible Ralsei is some sort of simulacrum of Asriel, but I'm not sure if that's a red herring. I'm still suspicious that it could be a performance from a fully cognizant Asriel, and that he would like us all to interact with the persona as a separate identity with its own history... (well, sort of... It all depends on how much Asriel and Kris are conspiring together.)

I find it interesting you think of their lives as very different... They're not in perfect parallel, but DELTARUNE feels more like an AU to me, where the same 'emotional beats' and 'themes' are carried through, even if there are various things that do not perfectly mirror. For example, the Dreemurrs are not royalty in this world, Toriel does not have an isolated life as caretaker of the ruins, and Asgore is not spearheading a war against humanity. I suppose there's a lot less 'extreme' tragedy present, since their children are living, they're merely divorced, etc. but it doesn't feel wholly out of place to see Toriel as a choir leader & elementary school teacher, while Asgore runs his flower shop, right...? It's apparent that they're still bound to have relationship issues, and have the inclinations that they did in UNDERTALE, with Toriel seeming stern in ways, unable to forgive Asgore for something he did, and Asgore clinging to the past pathetically.

The Asriel we see rending the universe apart at the end of UNDERTALE has been through many things — and I think it's important to note that you can only even process this at the very end of the game. You even have to experience a neutral ending first, before you even know that Flowey is Asriel, and WHY that even happened to his body...! Imagine if UNDERTALE were divided in chapters, and you had yet to see the True Lab, read Alphys's logs, watch the tapes about the plan, and more! The only thing you'd have known about Asriel specifically, was the tale that the monsters relay to you when you go through New Home. A tale that we later learn isn't even wholly accurate, as the monsters couldn't have known that Chara's death and SOUL absorption was planned.

There's no reason to assume there aren't vast depths yet to uncover about Asriel in DELTARUNE. Though... I'll also advocate for Ralsei briefly, since his 'backstory' IS supposed to be sad? He's a Lonely Prince; while the Dark Worlds we encounter are whimsical and the inhabitants are as well, it's not as if Ralsei has been best friends with everyone his whole life. He's been alone, in his castle, waiting for years, with no one to talk to, nothing to do but wait to service the heroes and fulfill the Prophecy. Currently, Ralsei is undergoing a questioning of identity, because of how empty his life has been... In reality, I think his constant gratitude and erm, insisted lowliness is pitiable. Whether we're interacting with Ralsei as an authentic being, or whether he's a performance from Asriel that encapsulates things he feels about himself, it's quite sad... He really does state that Darkners only exist for the fulfillment of Lightners, and he believes that he will one day be obsolete. He doesn't see a purpose in having any of his own hobbies, desires, belongings... Quite a sad, empty life proposed for our little Ralsei. We know Asriel in UNDERTALE felt alone without Chara, numb and hollow as a flower, unable to feel for anyone anymore, enough to attempt to take his own life. Asriel is a very dependent individual, who couldn't find purpose without his best friend there with him. If you observe Ralsei's behavior, he constantly turns to Kris for approval over the slightest thing. Even as he's wondering if he should be himself, have his own opinions, he's asking Kris repeatedly if that's OK for him. (Really, he can't even celebrate Kris having everyone's controllers un-scrambled in Ch3, without meekly saying, '...right, Kris...?') All seems cohesive to me-!!

Aside from UT Azzy, what we can learn about DR Azzy from dialogue/investigating the environment also threads well with Ralsei. To list a few things:

• Asriel was commonly seen as well-behaved. Ralsei is very rule-abiding and nervous about stepping out of line.
• Asriel sang in choir (well enough that Father Alvin feels that the choir is lacking without him.) Several of Ralsei's ACTs involve singing; his voice can soothe enemies to sleep, and he perfect combos his parts of Ch 3's rhythm mini games.
• Asriel used the knock-off controller, while Kris (more of a Gamer) used the proper one. Ralsei comments he's not 'supposed' to be player one, and has stated multiple times that Kris is good at games. It's likely their dynamic was one where Kris was the more serious player 1, and Asriel often let Kris take priority, deferring to their direction. (Also worth nothing that Ralsei often talks as though he's never watched movies and experienced the world, so I think it's odd he has an idea of his 'place' when playing video games, something he shouldn't have been able to do with anyone either...)
• Asriel was often doing things for Kris, suchas being willing to carry them to school in his arms, and getting hot chocolate with them after church even after the family stopped doing it. It's possible he kept pizza coupons on hand, as well as chocolate in his pocket, for their sake as well, as they're fond of ICE-E's and are a voracious eater. Paints a picture of a doting older brother that indulges Kris often... Which, is completely cohesive with the Ralsei promising to bake Kris yummy cakes (of their favorite flavors!), setting up tea parties, and in general prioritizing, complimenting, and supporting Kris.
• Asriel was concerned about 'sinning', even without external pressure from the religion. There's this sequence from an ACT with Poppup * Ralsei accidentally clicked on an ad for "lightners 4 darkners in ur area" and was mortified. * He deleted the browser shortcut on the desktop entirely... * ...but immediately felt guilty because he thought he had "deleted the entire internet". * I... I didn't mean to do it... I... I'm sorry!!! I repent!!!

• He's been shown using fire magic in an ACT done in Ch 4, very visually similar to the flames that the Dreemurrs all use in UT.

• ... AND WELL... VISUALLY... It seems that they're QUITE SIMILAR, enough that Susie could joke that Kris photoshopped Ralsei into a family photo, and Noelle (someone who grew up closely alongside Kris) could be confused by why Ralsei looks like Asriel. NOT A SMALL DETAIL TO ME... I JUST DON'T KNOW WHY THE ANAGRAM NAME AND SHARED APPEARANCE, IF ONLY TO NOT HAVE ANYTHING TO DO WITH EACH OTHER... I REALLY DON'T GET WHY THAT WOULD BE THE CASE......!!!!!!!!!!!

[unclenches my jaw.] [inhales...] So— in summary, I see lots of overlap in Ralsei and Asriel, in many layers. Narratively... personality wise...! In this current game, and in the previous one...! I'm quite certain we'll learn more about DR Asriel's suffering as the game goes on, assuming it has to do with agency, nostalgia/the inability to move on, and the issues of identity without Kris (how to live, be motivated, how to do anything without them?) I'm also certain he will be our major antagonist and villain...! The suspicious moments of Ralsei lying to us, the way he doesn't abide by rules other darkners do, his Big Dark Fountain that gets More Powerful every time we seal other fountains For Whatever Reason, the ominous door at the center of his castle with many sets of wings Kind of like the titans seem to have... Well, I have a feeling it's all going to come together. In some gut-wrenching way. ◉_◉ And we'll all be gobsmacked about it in SOME way, even with the intuition to see it coming. I'm excited and terrified, as a result. Haha.