Teyvat Story Integration – Experts are welcome to contribute.

Primordial One—Phanes—Heavenly Principle
The Sustainer of Heavenly Principle (key point: Sustainer, not the Principle itself), the one the protagonist encounters.
Supplement: There may be more than one Sustainer.

Nibelungen—Second Throne—Third Descender
The remains of the Third Descender are the Heart of God. It is known that dragons can be resurrected from their remains. The reason the Seven Archons divided the Heart of God was likely to prevent the resurrection of Nibelungen; its power was too great, such that even the Heavenly Principle had to seal it.

Why does the Cryo Archon seek to revive Nibelungen?
Because the world of Teyvat, like the dragon race, is doomed—both are fated for destruction. The dragons' world was destroyed because of Nidhogg; Teyvat faces destruction at the hands of an external calamity.

The "Rene Narcissus Cross" mentions this:
The world’s destruction has nothing to do with the whale. The Devouring Whale is just a monster, not truly dangerous. It was thrown over by Skirk's master to drink water; after consuming too much of the primordial waters, it swelled up.

With the water dragon gone and the first Hydro Archon perished, there was no one left to restrain it. The second Hydro Archon only possessed the water dragon’s authority, not its body, so could not suppress it. The first Hydro Archon was created from the water dragon’s flesh; without the dragon revived, she could restrain it. In the second Hydro Archon's era, Fontaine was destined for calamity.

Furina is just terribly unlucky...
She is a pure water spirit...

But, to return to the main topic:
Teyvat belongs to the world of calamity; it’s just that Phanes, the Primordial One, created a false sky—a kind of eggshell that protects the planet.

The sky is false, which is why there are constellations. The contents inside the Vision are not, as the dark readings suggest, for raising hens, but rather for recording. The Heavenly Principle knows that calamity exists beyond the world. If the eggshell breaks and the apocalypse arrives, after the world is destroyed and rebuilt, the records within the Visions can serve as a reference...

However, such records require the will of the user as a medium. If they are taken away and sealed, the user loses a significant part of themselves.

In the future, if the world is destroyed, it is suspected that certain people may be resurrected or replicated through the Visions.

Projection is also possible—this is just my speculation.

Are the Nails of Cold Sky punitive tools?
No, they are used to patch the false sky. They can neutralize the Abyss. The nail that struck Sumeru and created a vast desert was due to severe pollution; the one that destroyed Khaenri'ah was because the people there played with forces beyond control.

Why say that Khaenri'ah “played with fire”?
Because the people of Khaenri'ah were technologically advanced. Like Rene, they deduced the world’s structure and became aware of the calamity outside the world.

What is the purpose of the eggshell?
Hatching!
The false sky protects the interior, allowing life within Teyvat to gain power and grow continually. Naturally, the people of Khaenri'ah sought strength and growth, so they researched Abyssal technology, ultimately to protect the world.

But they went too far, the Abyss erupted, and the Nail of Cold Sky fell, destroying everything.

Yet, Khaenri'ah was not a complete failure—there were successes, such as Albedo and Melusine.

Albedo carries risks himself, and he has “Albetto” and “Albeevening”, but he is the most successful.

Some may not understand Melusine’s connection to Khaenri'ah. This race was born from the corpse of Elynas, with a different cognition from ordinary people. In some sense, they are Abyssal beings, but as they can coexist with humans, that is also a form of success.

Elynas was a golden creation, now sealed.

Currently, the Heavenly Principle’s purpose is to protect Teyvat, but its original descent and the war with the Dragon King remain uncertain.

Nibelungen’s reason for opposing the Heavenly Principle is simple: it seized Teyvat, a world belonging to dragons. Seeking revenge, Nibelungen obtained power from beyond the world and returned to battle the Heavenly Principle.

Why is it called the Third Descender?
Because Teyvat has an eggshell, the false sky. Although Nibelungen is a native, it was the third to break through the shell and enter, hence the Third Descender, and also the Second Throne.

People often confuse these titles, thinking the second is always second and the third always third, and that both Descender and Throne follow this order. In reality, this is mistaken. The Dragon King Nibelungen is both the Second Throne and the Third Descender.

What is the Second Descender?
Honestly, I don’t know; it hasn’t been specified. But it is likely the one who had a romance with the ancestor of the Seelie. The Second Descender was tragically murdered, their body divided into six parts—the story of the Six Dwarves. Coincidentally, all six dwarves hail from Khaenri'ah, with approximately these identities:
Prophet—Víðófnir
All-Knowing Wisdom—Irmin, King of Khaenri'ah
Supreme Power—Surtloki, simply put, the mentor of Childe’s master, Skirk’s master
Golden Creation—Rhinedottir
Changer of the Past—The Jester
Self-Exile—Dainsleif
The Second Descender’s divided body became six rings, including the one Dainsleif wears.

It’s still incomplete, and I’m continuing to organize it.
Exhausted...