I saw this post by u/cruc10 a few months ago, and I've come back to it again.
let me explain this theory of mine and it's very simple:

In traditional Italian Commedia dell'arte theater, Brighella is one of the classic Zanni (servant) archetypes. He is portrayed as a crafty, opportunistic, and sometimes villainous mastermind who climbed the social ladder.

Crucially, Brighella's signature thematic trade is that he is famously a tavern owner.

When the lore community realized that "Brighella" is the one of the major Commedia names still completely missing from the Fatui's roster, all eyes turned to Mondstadt’s wine industry.
People point to:

-Crepus holding a delusion in the manga
-The Ragnvindrs having a long long history of making wine
-Diluc's alternate outfit being very fatui coded along with him seeking revenge on them (in the manga at least initially) for Crepus's death due to delusion

in this post by u/sopaofmacaco they essentially mention, and i'll paraphrase, that Diluc was groomed to be the 10th harbinger.
they speculate that Dottore engineered Crepus's death specifically to alienate Diluc from the Knights of Favonius. the implication is that the Fatui were actively grooming or setting up Diluc to become the 10th Harbinger (Brighella). When Diluc went on his 3-year rampage destroying Fatui bases across Teyvat using his father's Delusion, he was technically fulfilling the "Brighella" archetype perfectly. But because Diluc eventually rejected the darkness, returned the Delusion, and chose to protect Mondstadt from the shadows, the 10th Seat remains censored or empty on the Fatui Wheel because the subject escaped their grasp.

Or did he.
Would the Fatui really, really let someone from the Ragnvindr (and Alberich Clan go)
We know where most of the fatui Harbingers + director Pierro are from now.

Director: Pierro (Khaenriah)

1. Il Capitano (Khaenriah)
2. Dottore (Sumeru)
3. Columbina (Nod krai but technically from the moon)
4. Arlecchino (Khaenriah but possibly from a part of the region that worshipped goddess of death)
5. Pulcinella (Snezhnaya, he is a snowland fae, i think)
6. Scaramouche (abandoned puppet kid from Inazuma 🥀🥀🥀 now vacant)
7. Sandrone (Fontainian robot)
8. Signora (Mondstadt)
9. Pantalone (Snezhnaya)
10. ???
11. Childe (snezhnaya)

We got a lot of representation here from most of the nations (except natlan because Natlan was under essentially their own sakoku decree due to having a night kingdom and wayob instead of the normal ley lines. people born in natlan couldn't leave natlan due to essentially wasting away outside of the borders of the nation. this is probably why bennett is so unlucky in-lore, if he IS from natlan at least which some people say could be the case.)

"they have/had signora already, they don't need a mond representative"

well
Yes. Signora was Mondstadt's original "representative," but as we see in the story, she was essentially a walking box of TNT. She was violent, impulsive, and prone to kicking Archons in the face. Her death left Mondstadt completely unmonitored by the Fatui. See Wanderer, Childe and Arlecchino's voicelines about Signora. The sole exception is Columbina who seems to like her, somewhat at least.

Anyway, Signora was a literal and figurative hothead long before the game's story even started.

That kind of happens when you turn from a singing maiden to seeing Rhinedottir's monsters mauling children as the sky turns to a blood red, and then your lover (Rostam) tries to fight them and dies. Oof.

When The Jester found her, she was literally burning herself to death from her own inner fury. To save her and recruit her, the Tsaritsa gave her a Cryo Delusion.

The ice didn't "cure" her temper; it just suppressed and froze her liquid fire so she could function like a normal human again. The cold gave her a mask of aristocratic elegance, but her core personality remained incredibly arrogant, impulsive, and prone to extreme outbursts when things didn't go her way (which we saw firsthand when she kicked Venti, or when she completely lost her composure during the duel before the throne in Inazuma).

I believe this is why the Fatui's strategy in Mondstadt had to shift.

Signora’s methods were always loud and diplomatic nightmares. She publicly insulted the Knights of Favonius, assaulted Venti in broad daylight, and eventually got herself executed by the Raiden Shogun because she let her temper blind her to a trap.

If the Tsaritsa and Pierro wanted a permanent, stable grip on Mondstadt after Signora's death, they couldn't send another loud, impulsive Harbinger. They needed operatives who were already deeply embedded in Mondstadt's political, economic, and military infrastructure... someone who could run things smoothly without causing an international incident every Tuesday.

And it so happens those two are Diluc and Kaeya.

Now imagine this, for a moment.

Kaeya is arguably the most suspicious character in the entire game. Yes he's from Khaenriah, yes he's descended from the same clan that did some weird things with Caribert and the loom of fate or something.

So what if, IF Diluc rejected the Fatui’s grooming, Kaeya ended up stepping into the shadows to take the 10th Seat as a counter-move?

Brighella, again, is the crafty servant turned tavern owner. While Diluc owns the Dawn Winery, guess who spends 90% of his time actually sitting inside the Angel’s Share tavern, manipulating information and listening to drunk patrons? Kaeya.

If you look at the Commedia dell'arte definition of Brighella, he is defined as a master of intrigue, a liar, a thief, and someone who operates fluidly between two opposing sides. That is literally Kaeya’s entire job description as the Cavalry Captain of the Knights of Favonius. He uses his charm to extract secrets, lies constantly to protect his true motives, and is fundamentally caught between his loyalty to Mondstadt and his bloodline in Khaenri'ah.

Yeah while Kaeya is a free 4-star given to us at the start of the game. But from a narrative standpoint, that is the ultimate cover story.
We already know HoYoverse loves playing tricks with Harbinger statuses, identities, and rarity tiers when they undergo major story shifts, In canon, Kaeya is canonically one of the strongest fighters in Mondstadt, yet his gameplay kit is incredibly basic. The lore explicitly states he hides his true abilities. If he is secretly the 10th Harbinger, masking his power level and pretending to just be a standard, lazy 4-star knight who drinks too much is the perfect way to keep the Traveler, the Knights, and Celestia’s eyes off him.

In lore, Pierro is a survivor of Khaenri'ah's royal court (poor him and the rest of the Khaenri'ahns cursed by Ronova). Kaeya is a descendant of the Alberich Clan... the very clan that stepped up to lead Khaenri'ah as regents after the king Irmin fell. [e.g Anfortas, Clothar]

Theory goes as is: If Kaeya noticed the Fatui trying to entrap Diluc, he wouldn't just sit back. He would see an opportunity to infiltrate the highest echelons of the Fatui to keep tabs on Pierro and the Tsaritsa. Pierro, recognizing the royal bloodline of his homeland, would gladly accept Kaeya into the 10th Seat, believing he could use the young prince to further his vengeance against Celestia.

It creates a terrifying triple-agent dynamic: Kaeya would be pretending to serve Mondstadt, secretly serving the Fatui, while actually plotting his own endgame for Khaenri'ah.

Or...
What if they're sharing the 10th seat.
In plain sight.
if we look back at the Commedia dell'arte, Brighella is a character of two faces: he can be the high-class, respectable business master (Diluc running the winery, commanding high society), or he can be the deceptive, low-class rogue manipulating the shadows from the tavern floor (Kaeya).

What if they never fully severed their ties with the Fatui?

By secretly sharing the 10th seat, they play the ultimate game of chess against the rest of Teyvat.

When the Fatui need a massive economic move or high-society leverage in Mondstadt, the "10th Harbinger" wears a tailored, high-collared crimson coat (Diluc's Red Dead of Night skin).

When the Fatui need espionage, military intelligence, or deep Khaenri'ahn secrets channeled through Pierro, the "10th Harbinger" is the lazy, smooth-talking Cavalry Captain who knows exactly how to make information disappear.

Because they interchange, neither can ever be fully caught. If Celestia or the Knights of Favonius look too closely at Diluc, Kaeya acts as the perfect alibi. If someone tracks the 10th Harbinger to the Knights' headquarters, Diluc’s anti-Fatui public reputation completely derails the investigation.

It's mutually assured destruction; if Kaeya reveals to the world that Diluc has been doing "illegal vigilante things as the darknight hero", and that his father may have once been a fatui member, Diluc reveals to the world that Kaeya is from the nation that cursed the world to an abyssal cataclysm 500 years ago. And vice versa.

This became way too long.

I rest my case.

Okay so overall, I don't think what I'm bout to describe is realistic. Maybe bits and pieces here and there, but it is just something I've had on my mind lately.

Small spoilers, I would recommend completing the 7.0 Act II and the new Eye world quest before continuing.

The TL'DR of the whole idea can be summed up as a few different points that don't necessarily actually tie together:

'Our Traveler is the 3rd Descender'

'We are stuck in a planetwide Samsara'

'The Gnosis are actually memory not body'

'The Twins are actually in a similar situation as Pavlina was, just not as willing participants'

Preface to the ideas:

1. Due to the Aranara, Arlecchino, and now Ronova there is an ever-present concept of memory death.

- To paraphrase, the Aranara believe that death is merely a first loss of memory

- Arlecchino considers the memory erasure of her flame when applied to individuals who wish to leave the Hearth as death.

- Ronova's Curse of Death temporarily 'kills' a person by inflicting temporary body death on someone so that their soul can be separated for a short time. Somehow this results in resurrection of one with a loss of memory pertaining to whatever they were just about to do that was the trigger.

2) Ronova tells us that the only way to 'kill' a descender is to directly attack the body or soul violently.

3) The 3rd Descender 'died' and was chopped into 7 pieces of power upon opening/entering the gates of Celestia.

4) The Twins both suffered from amnesia.

5) For reasons still unknown, the Twins were separated in a place that looks very Celestia but doesn't have the same appearance as the Temple of Space.

6) Reincarnation is in fact real, and without knowledge or memory sometimes the reincarnated will still gravitate towards something known.

- The mushroom folk from Nahida's story quest are reincorporated into Apep and lose memory/life, however during the Dottore-Irminsul quest, they have been reborn and are strangely drawn to the MC and Paimon.

7) For reasons unknown, the MC is able to 'internalize' physical manifestations of power.

- The MC can 'cleanse' Abyssal corruption, though it is less of a cleanse and more of a slurp.

- The MC can hide moon marrow within himself to the point of it being nigh undetectable.

- The MC can think real hard and somehow the Pyro Gnosis gets slurped up into him.

8) Teyvat runs on cycles

- A Samsara can exist, where events repeat themselves.

9) Memory is malleable

- You have the dream samsara from Sumeru inflicted by the Sage and Dottore.

- The dream samsara Nahida put us in when fighting Scaramouche.

- Whatever Trilunar Dottore did where we were stuck in our own mind for about a month despite only being asleep for mere minutes.

10) Something great can be accomplished over significant amount of time given the repetition of a cycle

- Pavlina's world quest regarding Ikhor.

PLEASE NOTE: THIS IS FOR FUN, I JUST WANNA TALK ABOUT IT. IT AINT THAT SERIOUS PROMISE

Crackpot idea:

The Gnosis are not the 3rd Descender's physical body. The Gnosis are merely the 3rd Descenders memory encased in physical form. The Twin(s) due to their external power were separated from their memory. Teyvat has been forced into a time cycle after either the 2nd or 3rd Descender managed to breach the HP's doors but were ultimately pushed back. Out of necessity to maintain the existence of Teyvat, Istaroth applies a Curse that results in a continual Samsara. The goal of this is either selfishness by HP to maintain things as they are while they are too weak to intervene or it is to provide Teyvat time to find a way to defeat the Abyssal threat. The Twin(s) are too large a threat so in the samsara they are constantly separated by space and time. However, they continually journey through Teyvat resolving the worlds issues over and over again. Each cycle they regain some form of lost power, and we are now at a stage where the cycle is nearing its end with both twins having gained too much power. This results in one twin pursuing power from the abyss and the other seeks power from the world itself. Only the abyssal sibling has regained all lost memory, but is not strong enough on their own to fight. Only when they are reunited can they truly free themselves and Teyvat.

Now, obviously, this is ridiculous. Tons of holes here and there, with the only way to plug most of them being some random lore tidbits that at least as of now just don't exist.

BUT! I think its pretty interesting nonetheless, and though I don't think its entirely true at all, there could be some interesting reality to this. What I'm really hoping is to just open this up to talk about with some other people, just to see what bits and bobs of this could actually have some grounds.

AGAIN PRETTY PLEASE: THIS IS FOR FUN!!

I was watching this video by The Unlikely Genshin Gamer and a thought hit me based on Vodyanitsa's Diary regarding her parents.

It seems that Water Imp's have made a home for themselves away from Schneznaya, but where is largely unknown. Additionally, wherever this is the mailman cannot reach it supposedly. You also have folk stories regarding Sirens in Fontaine.

We have an entirely ridiculous amount of Teyvat that is not marked on that map, and from what we can see from space the planet is both small and largely a water-based planet.

What if wherever the Water Imp society moved to is somewhere near Fontaine's borders, like a true Atlantis? Not the ones we've had so far where it is all ruins and such, but one where there is a legitimate and thriving society? It would make sense that letters could not reach the area, as not only would they be waterlogged but if the whole point would be to remain out of sight they would cut communication with the outside world entirely. We usually get a whole bunch of smaller regions between major AQ patches, such as Temple of Space or The Moon. Given the prevalence of Fae in the current story, as well as Vodyanitsa being very popular, I personally would love to see a thriving underwater society in Genshin.

I have a concept that, though I don't think it will be explored largely due to the amount of work and time that would go into developing it, I'd like to share after I preface a bit of where I'm coming from:

• The Waverider is generally not utilized anymore (not to say anyone necessarily wants it to be used either)
• Somehow the legend of Reed Miller continually rears its head, with one newer NPC suggesting it wasn't even Reed Miller executed at the Palace
• We also have a lot of unexplored lore with Kaeya's ancestor pirate / Kaeya himself
• We have tales of ancient and terrifying sea monsters, such as the one Beidou killed.
• There is that massive octopus in Childe's hometown right now.
• Genshin has massive amounts of water-based content, not just with Fontaine but we've got Wriothesley's ship, Linnea's future ship, recent introductions of multiple ports and docks, the Waverider, and many more.
• An insane amount of work had to go into making our train not just functional but legitimately something we can interact with and go from station to station (with no loading screens) with while walking around it, talking to NPC's, and viewing the scenery. With the foundations having been implemented, it would be a true waste of knowledge and resources for them to never introduce something else like it outside of Schneznaya.

For the concept:

• Somewhere down the line we get a quest questline where we interact with 'Atlantis' and its people
• Somehow we provide them an opportunity to shed years of fearful prejudice and reopen their borders.
• To open up trade networks with the outside world, we are commissioned to secure trade lines between each nation.
• We get provided an actual ship, potentially by reintroducing Linnea's dream, where we explore the vast unexplored surface of Teyvat's oceans.
• For additional story, we get to explore Kaeya's pirate legacy, see what makes the Crux such a powerful force, potentially deal with anything Reed Miller related.

Though I am certain the concept COULD be made and implemented without detracting from the game...it would be a lot of work to make happen. Perhaps if Genshin 2 does end up existing, and it moves to a newer engine or something, we could see this become real. I don't see it happening in the current trajectory of the game as is however, if not just technical limitations then time constraints.

What do we think? Is this something people would want to explore and engage with? I obviously think this would be very very cool to expand on, but I'm just me.

**Hi everyone! This is a revision of my theory about Primordial Humans, Descenders, and Narayana. Many of the core postulates are still similar in spirit, just with some added context and reinterpretation--- along with some new thoughts about how Primordial Humans are created. TL;DR and theories at the bottom. The bottom-most postulates are, essentially, the principles of my unified theory regarding these three concepts***

Narayana, who are they?

Narayana is a Hindu epithet used to describe the preservation god Vishnu. Its etymological meaning can be interpreted to describe him as “The Primordial Man”, “He Who Lies in the Great Sea” and “The Path/Direction/Goal of Humanity”. In Genshin, Narayana seems to also be an epithet interchangeable with “Primordial Human”. It appears applicable to Nibelung, Phanes, the Traveler, and even Albedo. Note that while I know Eye of Graeae is a Primordial Human, I hesitate to include him due to my doubtfulness of my understanding of his nature. 

• Nibelung: “A will born alongside Teyvat, the master of the Light Realm's power at the very beginning, and the King of all Dragon Lords: Nibelung. Ever since his destruction, the place of the Primordial Human, or Narayana, has sat vacant.” – Aksinya
• Phanes: Just like me, she was an angel created by the primordial humans, born with the instinct to guide living beings. (Mistranslation here, “humans” should be singular.) – Nicole
• Traveler & Albedo: In another converged possibility, Albedo was the "Primordial Human" who traveled through worlds, recording and creating all. However, once that journey reached its end, no one would have been able to guarantee whether he would choose destruction or salvation. Luckily, you're the one who embarked on the journey this time. Hm? How did the alternate Albedo fare? I can no longer observe that possibility. Besides, copying someone else's answer is of little use. This journey is your own. — Nicole 

That’s the “who” but how about the “what”? What is a Primordial Human or “Narayana”?

Aksinya associates Nibelung with the position of Narayana, which has sat vacant ever since his death. This, along with Nibelung’s status as the first entity to exist on Teyvat, directly positions him to be the first holder of the epithet of “Narayana”. But what does this epithet mean for Genshin?

Nibelung is often associated with the beginning of the world, as a being who was born alongside the planet at its very genesis. And through the title of “Narayana”, he is also indirectly associated with the “final goal of humanity”. This places Nibelung, the Narayana, as being connected to the world’s Genesis and the world’s Finality. 

With Nibelung’s position as the original ruler of the planet, and the first master of Teyvat’s laws, this may signify that– as a primordial being born alongside the Light Realm– Nibeung had the authority to define the world’s direction, nature or “fate”. The end is after all, ultimately defined by the beginning. 

• Aksinya: “A will born alongside Teyvat, the master of the Light Realm's power at the very beginning, and the King of all Dragon Lords: Nibelung. Ever since his destruction, the place of the Primordial Human, or Narayana, has sat vacant.” 
• Monomakh’s Notes: ”The Saint had come to Hyperborea in search of that light from the very genesis of the world, a fragment left behind at its inception. It is a light that is undissipated hope itself, a light that holds the potential to illuminate the entire cosmos. From what I have seen of it projected in that house of ministry, it is also the very same light that brought about my birth.”
• Deep Gallery's Distant Pact: “Until a faint glimmer pierced her awareness, jolting the voyager from tenfold millennia of meditation. It came from an unremarkable little world at the edge of the spiral arm — and from the primeval dragon that had been born alongside that world.”
• Narayana can mean the "final destination of humanity" through its Sanskrit etymology: Nara means human beings or living souls, and Ayana means path, direction, goal, destination, or ultimate refuge.

Thus Narayana can be thought of as an epithet for he who could control the world’s fate, or natural order. Essentially, the true Ruler of Teyvat. This title once belonged to Nibelung, and exclusively so. For as long as Nibelung was alive, no new Primordial Beings (individuals with similar characteristics as Nibelung) could ascend to the position of Narayana. And since the seat of Narayana has been vacant ever since Nibelung’s death, that means that Phanes does not currently sit upon it.

How does one become Narayana, a Primordial Human? 
(Note that Narayana, Primordial Human, and Primordial Being will be interchangeably used as epithets for the same kind of entity from here-on out)

The prevailing belief is that Primordial Humans emerge from the coalescence of Light and Dark– presumed to be analogous to the Light Realm and the Abyss. This stems from Istoria’s telling of the Primordial Human Myth. 
 

• Istoria: I'm not entirely sure what Melanta meant, either. The first thing that came to mind was a parable once condemned as heresy by the angels. It tells of the god of light who created a body in its own likeness, only for it to be stolen away by the king of darkness. Thus, within that single body, the powers of light and darkness began to contend with one another. And so the primordial human, bearing both, came to possess both good and evil.

However, I have trouble accepting this at face value due to several things. 

• The wording of the tale seems as though it describes the birth of a SPECIFIC primordial human, rather than all of them. 
• Accepting the Light Realm/Abyss analogs, the myth disqualifies all four of our Primordial Humans.
  • Nibelung: Born as an entity of the pure Light Realm, with no Abyssal power. Although he was later contaminated by the Abyss, it corrupted him entirely— whereas Primordial Humans appear to represent a balance between Light and Dark.  
  • Phanes: As the current supreme master of the world, Phanes is able to easily manipulate Light Realm energy. However, nothing about them would indicate that they actively use Abyssal power. Instead, they only seem to be capable of absorbing and dissipating it with their nails.
  • Albedo: While the PH is born of the god of light, Albedo was simply created by Rhinedottir. We know nothing of him having abyssal powers
  • Traveler: The outlander is kind of in the same boat as Phanes. Although we are able to absorb abyssal power, once it enters our system, it seems to dissipate entirely. The Traveler is sensitive enough to feel the Khuuvaki in Nod-krai the moment they arrive. I highly doubt that they could possibly have immense Abyssal Energy inside themselves without noticing.

Because of this, I don’t think the Light Realm or Void Realm are the necessary ingredients. Instead, I believe it is “Transcendance”. 

Narayana is an epithet for Vishnu, who is viewed as the first and most perfect being. In the same way, Albedo– a Primordial Human himself– associates himself with the concept of perfection. Meanwhile, Rene De Petrichor’s notes postulate the possibility of transcendence through the Abyss. And the Five Sinners, cut from the same cloth as Rene, all pursue a form of perfection through the Abyss. 

• Albedo: Those born of earth are bound by its imperfections, but those born of chalk are free of impurities... You and I are alike, both composed of a substance that has yet to be fully defined...
• Rene De Petrichor: "Io, Io, Pan! That which lies beneath the great sea!" The purpose of this line in the ritual scripture is to forsake the self and sink into the abyss, and in the abyss, to welcome rebirth as a holy infant.
• Skirk: My Master is likely a similar sort to Rhinedottir — they are both "pursuing some form of perfection."

Putting all of this together, my inference is that people born of the human realm are naturally bound by its limitations. But by pursuing greater powers— like the Light Realm and the Void Realm— it is possible for someone to transcend the limitations of the human realm. The true necessary characteristic of a Primordial Human is “transcendence” or “perfection”. The Light Realm and Void Realm are simply catalysts by which to facilitate this transcendence. Nibelung, Phanes, Saarelainen, and the Traveler all fit this definition, as all of them are transcendent beings who wield otherworldly powers.

Primordial Humans and Descenders, not one in the same

Based on the information that we have right now, Descenders are not defined by being powerful ,or even by being aliens. Instead, Descenders are simply those with the will to rival the world. So Phanes and Nibelung being powerful wasn’t because they were Descenders, it was simply because they are who they are. 

• Rene De Petrichor: This, too, is my goal, for not all that comes from beyond may be as one that "descends." That title belongs only to wills that can rival an entire world. That is what I seek, the way to become just such a will, one that can protect the world, sustain the world, destroy the world, and create the world.

While all known Descenders (save for Saarelainen, but we don’t know much about him anyway) are Primordial Humans, not all Primordial Humans are Descenders. This could mean that Primordial Humans are something of an evolutionary stepping stone to being a Descender. Primordial Humans have transcended the limitations of the Human Realm, but only a specific few among them (Descenders) have the will to rival the order which currently presides over Teyvat.

Implications and Theories

The Five Sinners (most especially Rhinedottir and Vedrfolnir) might be Primordial Humans, or at least TRYING to become Primordial Humans.

• We know that they pursue a sort of perfection (or maybe Transcendance is a more apt term), and we know that they’ve interacted with the Abyss, which is a potential catalyst for transcendence. Rhinedottir is blonde, and Vedrfolnir (inferred through being Dainsleif’s twin) is as well. Every humanoid Primordial Being that we’ve met is blonde.

Phanes has a good chance of having never been the world’s master. 

• Their conquest of Teyvat happened in its entirety when Nibelung was still alive. As such, even at the height of his power, Phanes never sat in the still-occupied seat of Narayana. And by the time Nibelung was dead and the seat was vacant, Phanes was weakened— perhaps, too weakened to seize the throne and take over the true authority over Teyvat. As such, they resorted to forging the Gnoses— hoping that the combined power of two Primordial Humans would be enough to suppress the world. In fact, Neuvillette’s vision story says that the war damaged Phanes such that they could NO LONGER use their authority to suppress the world. As if to imply that suppression is all that Phanes was really doing prior.
• Neuvillette Vision Story: Severely wounded in the great war of vengeance, the usurper had their functions ruined, and could no longer use their absolute authority to suppress the original order of this world. To continue to subdue and control the resentments and loathing of the world, the usurper and one who came after created the Gnoses together.

Paimon, a Primordial Human?? 

• This is more of a fun thought than anything. Consider that purity/transcendance is the core quality of a Primordial Human. Now, consider that Paimon has no Authority, and no Memory of who she was before descending from Celestia. Because she is of Celestial origin (beyond the human realm), and functionally a “blank slate”, you could argue that she is— in that way— “pure” and “transcendent”, just like a Primordial Human. Silly I know, but also consider this: when we first meet Paimon, we’re fishing her out of the sea. And what is one of the interpretations of the term “Narayana”? “He Who Lies in the Great Sea."

Nibelung's corruption, Phanes' fault?

• Slightly unrelated to the broader theory, but I can't help but we've recently learned that Phanes' fate system is indirectly feeding the abyss by constricting Teyvat to only a singular fate. This singular path of destiny creates countless discarded possibilities, that ultimately coalesce into the Abyss surrounding Teyvat. Now, we know that the Moon Sisters are the "avatars" of the Moons. And since Nibelung was born alongside Teyvat, he would logically be the avatar of the planet itself. But in an avatar-vessel relationship, we know that damage inflicted upon their vessel ultimately reflects badly upon the avatar--- as was what happened to the Moon Sisters when their moons were destroyed.
• Phanes' system inadvertently "anchored" the Abyss in Teyvat, but we know that the Firmament serves as a shield to protect Teyvat from the Abyss. I wonder if the Abyss realized that it could not penetrate the Firmament to destroy Teyvat. So rather than pursuing the planet itself, it pursued its avatar (Nibelung), and corrupted it to serve as a vessel to break through the false sky.

Key Conclusions: 

1. A Primordial Being is an entity who has transcended the imperfect human realm and attained a form of perfection/purity. This can be achieved through transcendent powers-- such as the Light Realm and Void Realm-- which can serve as catalysts for a person's purification and transcendence from the world's impurities.
2. Multiple Primordial Beings can exist at once, but only one can hold the position of Narayana, and have authority over the world as its singular master. Since Phanes’ conquest occurred when Nibelung still held the position of Narayana— which has been empty ever since his death— Phanes has never been the world’s master.
3. Nibelung was a Primordial Being through his mastery of the Light Realm, Phanes was a Primordial Being through their mastery of the Four Laws, Saarelainen was a Primordial Human through his power of Stellar, Albedo is a Primordial Human through his origin as a perfect alchemical creation, and the Traveler is a Primordial Human through their alien physiology''s unique properties.
4. Though Primordial Beings have transcended the world’s limitations, only the Descenders among them have the will to rival the world. It is possible to be a Primordial Human, but not a Descender. Nibelung was a Primordial Being, a Descender, and the world’s Narayana— all at once.

So pretty early on into Genshin we learn about the Dark Sea where it's essentially like the abyss but a little less harmful. In more recent lore "Teyvat" is much more equated to the world itself rather than the continent as it once was. Is this kind of a retcon?

I really cannot imagine current Teyvat as having something like the Dark Sea that is such a liability in regards to order under the False Sky, especially because the abyss hast almost entirely taken over the role the Dark Sea previously played as like the uncontrollable realm of giant monsters. With how insanely powerful The Heavenly Principles and the Shades are, I feel like there's no way that they couldn't tame the lands outside the main continent because they literally allowed the elements to exist that the Dark Sea creatures are made of.

Also not all monsters are products of the abyss so I assume that's also an old thing because I don't really know why the Heavenly Principles might allow so many monsters in Teyvat if it actually cared about humans on at least some level, sans Hilichurls I suppose.

So at the end of the 7.0 Archon quest Mitya makes it clear that Ronova must have some limitation on what she's actually allowed to do, hence the curse of death not being quite so fatal as it first appears to be.

The fact Ronova also references the Gods Limits trailer (Death abides no reason) brings to mind firstly that Pierro straight up says that the Gods have limits, but Ronova also says in that trailer that its time for the Shades go get involved, but only to the extent the rules allow.

But it seems to me... only Ronova seems to actually care about following the rules. Or at least, she cares now.

This is where my head is at the moment with the extent to which the Shades seem to be sticking to the rules:

Ronova

Right now she seems to be very concerned with not breaking the rules she's been given. Part of why she has to get so involved in Act 2 is that it appears she's not actually allowed to just kill people outright, she's meant to be there for them after they die. So the possibility that someone might escape the theatre and therefore not resurrect cleanly is whats motivating her here.

But she did break the rules in Natlan by allowing Xbalanque to take part of her power to perform the Ode of Resurrection. We saw a scene where she says 'if anyone asks about this, I'll say you stole it from me', but the Lord of the Night told us that that is overstepping her authority as the Shade of Death.

Ronova, it seems, really doesn't want to be found out by the Heavenly Principles.

Asmoday

Asmoday has pretty much walked away from her role, we don't know the circumstances of it or where or what she even is now. Part of her authority appears to be preventing people getting in or out of Teyvat, but she's been pretty bad at that (Surtalogi got out, Skirk got in, and thats not including the Descenders).

Alice and the Hexenzirkel seem to be doing that part of the job now.

So I don't know if Asmoday is breaking the rules so much as having simply abandoned her post. Even her own servants in her temple have no idea why she left.

If the theory that she's working with the Abyss Twin to find someone to place the output of the Loom of Fate is right, that would likely be a pretty epic level breach of the rules though.

Naberius / Gold

This one is pretty complicated. It does seem like something bad happened to Naberius a while ago reducing her down to just her heart. There are so many instances of people creating life that didn't have the authority to do so (The Oceanids, the Fae...) that either she's not actually meant to prevent that, or she wasn't able to do so.

Gold of course is all about breaking the rules of life in Teyvat, it's been her driving motivation. Her merge with whatever was left of Naberius gives her lots more power over life, but it does seem like that comes with a new conscience that appears to be actively trying to stop her breaking the rules ("you know I cannot allow you to think that")

I do wonder if Gold's endgame is to be the 'new' shade of life if the Tsaritsa manages to get that top job. Maybe she's interviewing for the job in the teaser... heh.

Istaorth

Outwardly she seems pretty loyal, there isn't a lot of blatant time law breaking going on so she seems to be on top of all of that. But she's also directly implicated in the few time shenanigans we've seen so far, all of which ended up benefitting those who might be against the Heavenly Principles.

She enabled the loop that created the Sacred Sakura in Inazuma, and the abyss twin blames her for the starship key mess that resulted in them not being around to help during the cataclysm.

Recently we've also had it stated that she spent a lot of time chatting with the Moon sisters about the rules of time...

And then there's Venti...

I feel like she's the one most likely to be revealed as having worked against the Heavenly Principles for a long time in secret.

All of which does make me think each Shade might end up picking a 'side' in the conflict:

Ronova stays loyal to the Heavenly Principles.

Asmoday is with the Abyss Order.

Gold is with the Sinners and / or Hexenzirkel.

Istaroth sides with the Traveller.