Time for a long Aylin ramble, because I haven't indulged in a while.
I'm actually really invested in Aylin being an aasimar! I do not think it is a misnomer or mistake, as I've seen people suggest. She was referred to as a celestial explicitly in some older builds of the game, but this was changed at some point during development. And I noted aasimar enjoyer Oath, quelle surprise prefer it this way for a variety of reasons. Primarily, I think, because it lets her be larger than life, have a touch of that other-worldliness and otherness, while keeping her very much "of this world" still, very (physically and otherwise) present and part of the prime material plane, and ultimately far more human than I believe even she herself would sometimes like to be.
To bring up the most basic and rules/mechanics-bound "creature type" level of categorisation, as an aasimar she is a humanoid, and not a celestial - outsider. Her outsider status is absolutely there and a goldmine of things to explore, but that's a different post sitting in my drafts for far too long that I'll get around to one of these days (but for now you should read this post that I love). Yes, she is in a very real sense above it all, she will outlast everyone around her and whatever she gets involved with. We also get to see her dramatic poetic archaic speech idiosyncrasies (Ho!), her odd sense of the passage of time, and, of course, her oft-discussed and joked about apparent lack of filter or regard for current social graces.
(Endlessly amused at her just going: I'll do it when my mum tells me to.)
All things combined, Aylin feels more like a being of two worlds to me than a guest visiting this one, even as she is called the emissary of a goddess. She embodies a blending and an odd balancing act between the lofty divine and the mundane, duty and preordained purpose and personhood, and touches on the many ways this balance can be tipped. A classic D&D aasimar struggle, really, and a well I am happy to keep returning to.
Balthazar: She was a unique specimen even before I began my work. Aasimar. A god's blood united with mortal flesh.
She honestly isn't even that far from a regular aasimar stat- and ability-wise - Aylin does have several special abilities, but these are flavoured as blessings from her divine mother instead of an inherent property of her as a creature - though, notably, Aylin herself at one point claims she is always reborn because "it is [her] nature".
“Blessed with the favour of a goddess, Nightsong cannot be permanently killed. When unconscious, at the start of her turn she recovers 1 hit point.”
“Nightsong will be resurrected by the powers of Selûne whenever she dies.”
Importantly, she does not get to reincarnate, or get a new body, or flit away to her "home plane" or anything like what celestials get to do. She is anchored to this one physical existence (again, very human of her), tied and limited to this one body as it painstakingly repairs itself over and over and over (to a sometimes extreme extent, e.g. the all but outright stated regrowing of amputated body parts in a frankly horrifying context), insistently and indomitably but ultimately imperfectly. And I think that's part of why the kintsugi design drives me utterly wild, why her immortality setup is more interesting to me than, say, a mutant healing factor, or something like the characters in The Old Guard. Her history is pretty literally engraved on her skin, and when she, in the role of a power-granting artefact and the object of a ritual sacrifice, tells you she will feel every wound you inflict upon her, it is so easy to believe her. And I'm not even that invested in physical suffering, just that it means it's all still very palpably there, forever, and she doesn't get to magically restart with a clean slate in this sense, nor does she get to forget past lifetimes as some creatures like devas do. It's just a flavour of immortality I personally find far more engaging than most.
(I mean, yes, I am also a known hurt/comfort sucker and if you're going there in order to set up a scene where she's, I dunno, getting doted on by Isobel who's invented new scar tissue pain relief massage techniques, you know I'm going to be all over that.)
I'm also not sure I'd say she can just pop over to Argentil to hang out with her mum at will. I mean, planeshifting is not that hard to achieve, and also she can just… ask Selûne, ultimately, I guess. But I wouldn't say she has spent much time there, and I think she takes her role as Selûne's champion and representative in the Realms too seriously and too much to heart to be away from them for very long.
Which also calls to mind the issue of the obvious and "simple" answer to Isobel's eventual death - namely that with Isobel picked up as a petitioner soul they'll all just go live out the better part of an eternity in Selûne's realm. Probably in some form they will - it's never guaranteed, but this time, yeah, probably something like that will happen, and there will be, as Melodia says, no loss, only temporary separation. But I'm really not into just handwaving or stripping away most of the mortal/immortal pairing issues inherent in the relationship. If we're going for the "hang out in a different plane of existence forever" option, I think at one point Aylin would have to "complete" her duties and lay down her sword, in a way, and pick between Faerûn and the Gates of the Moon - meaning she herself is effectively moving on to a completely new phase of her existence as well.
And while Selûne carving a lovely marble statue and bringing it to life and similar takes are fun and beautiful and interesting, I'm very invested in an Aylin who was born, raised, and had to actually grow up and learn and be trained. I have a ton of headcanons of Aylin being a weird glowy baby at some point (with all the Disney's Hercules jokes I've seen folks make, of course), being entrusted to a series of Selûnite enclaves and temples and cloisters, hounded by Shar and her agents pretty much all her life.
(Neither here nor there, but Aylin also comes off as a fairly "young" immortal to me - note that I am basing this on absolutely nothing but a general impression and there's no actual hint anywhere about how old she really is. Just vibes.)
To finish up, I'd like to shout out Isobel, and the big humanising factor she is presented as. For instance, a very concrete bit of motivation for Aylin to eventually "humanise" her perception of time, if nothing else.
Aylin without Isobel is horribly depressing to me mostly because she seems to distance herself from her humanity and err on the side of holy duty (see: her epilogue letter, ouch). And Isobel is definitely the person who (invaluably, imo) explicitly and consistently insists on Aylin's humanity and personhood, who cares for her as a woman and not a divine weapon, who actually treats her well-being as a priority, and who understands her so very well and so deeply. Who does acknowledge the gloriously resplendent Dame Aylin, daughter of the Moonmaiden herself in all her awe-inspiring presence and occasionally amusing foibles, but who never fails to look past the titles and fronts even Aylin herself is so keen to put up, and focus on what lies behind it all.
A moment that sticks out to me in particular is her bemoaning Aylin's disregard for her own safety, then actually getting very angry if you suggest Lorroakan can't hurt Aylin:
Isobel: Even after all she's been through, she thinks herself unstoppable - invincible. It all feels like recklessness to me.
Player: Lorroakan can't harm her. Have faith.
Isobel: He can harm her. Just as Ketheric did. She'll survive it, but she can suffer like any of us - and for longer.
Using Isobel's words verbatim is a good conclusion to my thoughts here, I think: the truth of Aylin being "singular among us all" coexisting with all the ways Aylin is "just like any of us".
And now I'll pay the cute Aylin screenshot tax one last time.