Paimon is Koitar, or at least related to her.... hear me out I may not actually be crazy.
Disclaimer: I’m not too much of a lore nerd, just had a theory and did a dive into lore and may slightly be going insane. And spoilers for Echoes of a Forsaken Song (Amsvartnir world quest)
So the Paimon is a seelie/angel theory is already out there, she floats, calls herself a guide and has aesthetic ties to celestia and the heavenly principles, creator of the angels. I don’t believe that Paimon would be either HP or Asmoday as I know is commonly believed, as I believe the devs wouldn’t tease something with such impact on the lore and story with obvious aesthetic design choices, everything tells me it's a red herring.
Now what caused this theory:
I was doing the world quest related to Koitar, Echoes of a Forsaken Song, and noticed when you play the lyre, Paimon states that she cannot hear the Lyre, thinking it’s broken, meanwhile the traveler hears it. This is the same when Paimon attempts to play the Lyre. Now this could be that it's a case of with the traveller being a descender, there could be some Irminsul-esque shenanigans going on where no one from Teyvat can hear it. HOWEVER: A Drunkard’s Tale Vol.3, in reference to the Royal Court states that others can hear it too: ‘It is said that to this day, adventurers who pass by this place still hear a strange yet harmonious melody sounding from within’.
So why can’t Paimon specifically hear the song??? It's clear Koitar lost her memories due to HP’s punishment, but as far as I know it wasn’t explained exactly how, and I suspect that it could be a case that Koitar was essentially banished from anything from her past, explaining why Paimon may not be able to hear it. It is also mentioned in the artifact Deep Gallery’s Moment of Oblivion also states she lost her name and form, which would explain why she has the new persona of being Paimon.
Another thing to note is that the angels wore crowns that acted as shackles to HP. Ofc, Koitar’s shackle broke upon learning forbidden knowledge, but who’s to say she couldn’t be shackled again? Paimon has a crown on by the way, just saying. If it is a shackle, maybe it's what prevents her from hearing the song so old memories don't come back.
Another theory I had with crowns is the circlet of logos part of the artifact sets. Ofc the first 4 represent the shades, but I’ve heard that the crown is meant to represent HP. But if the other 4 artifacts represent the creations of HP, why wouldn’t the 5th follow suit and be the other creation of HP, the angels. Why do I bring this up here though? Something has been on my mind since the start of Nod Krai, where there was a humorous line where Ineffa rates Paimon’s power as ‘1/5th’. A FIFTH OF WHAT INEFFA??? A FIFTH OF HP’S CREATIONS MAYBE?
But then why would Koitar follow the traveler? Well, it's fitting for the first angel, a race who naturally want to guide humans, to follow probably the most influential human currently on Teyvat, but there’s more to it. In the writings within the royal court, Koitar writes ‘...I will return to my own lands and wait for the star beyond the stars, the one who holds my liberty in thrall.’ The Twins have been represented as stars a lot, so she could be referencing them here, planning to meet them in the future. As to how she would know who they are, I don’t know, but the mural that appears on the end of the quest does have twin stars, likely representing the twins’ arrival. Maybe she knew that she would lose all of what she was and would become the Paimon we know today, and placed her trust in the Traveller, hoping that by traveling alongside them that they could free them from HP.
That or HP just lobotomised and shackled her to spy on the Traveller who knows.
Anyway, this is the result of frantic excitement now at 3am, so probably I have missed some critical detail and possibly this whole thing is absolutely flawed and I have wasted 2hrs of madness. Please comment any counter arguments, or even better if there’s more supporting evidence! Either way, I think I do firmly believe that Paimon is related to the angels in some way.
Or maybe she is just Asmoday idk.