Sup, it's been a long time coming, but part 2 is here at last, yippie! Before we get to the new content from both Amphoreus and Nod-Krai, let's take a look at Kephale, since I missed some pretty important stuff in Their lore. As we all know, Kephale is the previous incarnation of the Chaos code, right before Phainon, and before they ascended to Titanhood They shared the exact same name as him - Khaos. As the previous version of Phainon, Their lore is also applicable to this theory.
There's a lot to unpack here: first of all, we learn that the Three Fate Titans (Oronyx, Talanton and Janus) who were created by Kephale were also referred to as the "Three Fates sisters", which already paints a conntection with Nibelung's Three Moon Sisters, since both were based on the Three Fates from Greek and Norse mythologies. Secondly, a strand of Kephale's hair was the seed that gave birth to Cerces, the Titan of Reason, who's original form was that of a giant tree. The Irminsul, the World Tree of Teyvat, was created by Nibelung.
The Ley Lines, which are Irminsul's roots, are based on the concept of Dragon Veins from Feng Shui.
During the War of Funerary Flame, Nibelung attempted to regain control of his world and defeat the usurper using the Abyss that corrupted his body, and burning the Irminsul. Phainon's own body became corrupted as he became a vessel for the Black Tide/Irontomb, and although for a different reason, he burned Cerces, the very tree he created as Kephale.
Both Cerces and the Irminsul are giant trees located at the center of their respective worlds (Irminsul being the center of Teyvat, Cerces being located right above the Scepter's core layer) that are assosiated with wisdom and reason, and both serve as the source of information that stores memories and records about the history of their worlds.
It was Nibelung who brought the Abyss to Teyvat and used it in the War of Funerary Flame in an attempt to regain control over it, just like Chaoz666 reacted with agression after another inorganic being tried to take over it's computional power which resulted in Nanook gazing at the Scepter. That event ended up bringing the Destruction to Amphoreus, as well as causing the birth of the corruptive Black Tide.
Nibelung pierced the False Sky created by the Heavenly Principles. Just like Phainon.
In 3.6, we learn that Phainon turned his body into a seal to shield Amphoreus from the Black Tide and helped Dan Heng pierce through Evernight's Memoria tide of Oblivion. Sounds familiar?
A lot of the wording used to describe Nibelung is very similar to that used to describe Khaslana. They both started out as "noble heroes" who greatly loved and cherished the world and their companions, only to get corrupted by a dark force (the Abyss and the Black Tide) and become it's vessel in an attempt to save those who they cherish, which led them to become cruel, bloodthirsty and cosumed by firey wrath, hurting the people and the planet they wanted to protect.
Kephale has a laurel crown resting upon Their head, and Dromases, the dragons of Amphoreus, mimic said crown's apperance with their horns. Dan Heng, who is also a dragon, gained Kephale crown-shaped horns when he became an Amphorean Demigod as well.
This one is likely a coincidence, but Terravox, the King of Dromases, has their horns shaped unevenly, in the same way as Diabolic Kevin and Vigethos (Chimera Phainon).
Now, while Lygus and Phanes aren't as alike as Phainon and Nibelung, there are still some similarities between them, especially when we take a look at their relationships with Phainon and Nibelung respectively.
First of all, they are both represented by the concept of "Logos" and "Reason".
They are also the ones who separated the worlds they invaded from the rest of the Universe. They also both refer to those worlds as "microcosm of the world/cosmos".
(In case it wasn't clear: no, Zandar did not create the Scepter, despite δ-me13 being Nous's divine corpus, it was a creation of Rubert II. Lygus himself admits that, calling it "a weapon of war, forged by the emperor").
While the Flame Reaver did commit truly henious and awful acts, blinded by his fury and hatered, the Black Tide being tied to him and following him whenever he went, he ended up regretting all of it deeply once he calmed down. The destruction and death he spread brought him enormous pain. Just like Nibelung, the devastation he caused was done in a frenzy of wrath, rather than as a deliberate, planned punishment.
(note: I am NOT trying to justify Khaslana's actions here or paint him as someone who had no other choice, merely pointing out the difference in how his mindset for causing destruction is rooted in his strong negative emotions rather than calculated reason).
Phanes and Lygus however actively enjoy the feeling of control they gain from opressing their subjects and keeping them in line with inhumane punishments, as their cruelty is rooted in their obsession with enforcing their dominance in order to escape from their own paranoida abd fear that binds them.
As we know, Phanes stole the power of the Light from Nibelung, as well as his bow and, uh, almost everything. They were even called a "False Sun".
The Four Shades were also created using Nibelung's stolen power, as he was the one to bestow the authority over Time, Space, Life and Death to the Three Moon Sisters, who were his creations.
And as we see, when using Nibelung's stolen power to create the Shades, one of the results was Asmodey, who looks just like the Herrscher of the Void form of Kiana Kaslana, Kevin's descendant.
In the Summertide Scales and Tales event, we discover a world created by the Hexenzirkel Witches called Simulanka. We learn that it's mimicking Teyvat itself and it's fate. The four Teyvatians visiting it (Nilou, Kirara, Navia and Wanderer) correspond to the Four Descenders, while Mini Durin represents Nibelung himself (from the time before he became the Second Descender).
Everything that Mini Durin touched turned into cubes, similarly to Black Tide.
Once Mini Durin became human, his design retained some of his draconic features. These very features are very similar to those of Diabolic Kevin.
Just like Nibelung, Simulanka Durin has the power of the Abyss sealed within himself. In the Schicksal Archives, Diabolic Kevin is compared to an "abyssal demon".
There are probably some details that I wanted to include here but forgot, and there are probably details that I have missed. There is more content to come, about both Nibelung and Phainon, and only time will tell if my analysis was right on the mark or missed the spot. As always, feel free to add onto this post, either supporting or debunking my points, but please do so politely and in a civilized manner. I sincerely hope you enjoyed this read, even if you disagree with it, and thank you for reading this long nerd out of mine!
Huge shout out to @cap00chino, who provided me all the screenshots from the Simulanka event and pointed out the connections between Nibelung and Simulanka's Durin. They are the reason this post exist at all, since they were the first person to enlighten me with the possibility of Phainon sharing traits with Nibelung, back when his animations leaked before 3.4 even came out. I then kept my eyes peeled and gathered all of this lore to create an analysis on this topic, and that's how this huge wall of text was born. So thank you, friend, for the support you provided here <3