The last Dainsleif Archon Quest gave us so much more to the story of the Teyvat before the game's start. (And I would have told you guys all about it sooner but I needed to get my We Will Be Reunited theory out to you guys first to make any sense lol)
Previously we knew that there was a thing called Celestia where maybe a Phanes lives that set up the world order with the Seven who are chosen Archons that reigned over their own regions. Outside of that order were other regions but they did not sit well with Phanes or its Heavenly Principles. We still don't know a definite answer for that but we do know that these kinds of regions end up erased from history. Sal Vindagnyr for example was wiped out one day and we don't technically know why. Enkanomiya was sunken into the sea because it had legends about Phanes that it didn't want getting out for some reason. And finally Khaenri'ah attacked and was then razed by the Archons under his orders but we don't actually know why it attacked in the first place. I do have theories for all of that as you guys know but nothing's confirmed yet.
While the new quest doesn't help us answer these questions any better it does give us more details on what Celestia did to the people of these places.
From my theory I brought up that hilichurls come from the Gnostic word Hylic or the lowest form of humanity who can never attain the gnosis. From this quest we know that this is exactly true and it was a curse designed to punish the people. The worst off were these civilians who didn't have a strong enough resolve to even maintain their sentience.
But another angle we can think about the curse is Kaeya. He hides his eye and doesn't tell us why but now we know that Khaenri'ahns including those that became hilichurls hide their faces to stop themselves from having to look at what the curse did to them. This could be why Kaeya does it. It could even be just symbolic. Since he was a child when he was adopted by Crepus he seems to be a modern generation Khaenri'ahn, their last hope especially since he is their prince.
On the other hand if he does also have the curse then there's 2 ways that could have played out. One way is it could mean that even the children of the Khaenri'ahns affected inherited the curse and that's even more reason why Lumine and the Abyss are angry with the Archons and Celestia. The modern generations had nothing to do with Rhinedottir and the Cataclysm. (To compare you guys can think about Miroku from Inuyasha who is the 3rd generation cursed with the Wind Tunnel.) The other way is that maybe Kaeya isn't as young as we think he is. We don't actually know the whole story just that he was adopted and he wasn't in any actual danger when it happened.
What if the real reason Diluc can't forgive him is because he used some shady Khaenrian tech/Khemia to brainwash Crepus and Diluc into thinking they adopted him one cold rainy night when really he was a plant placed in Mondstadt by King Alberich? What if the reason he was Khaenri'ah's last hope is that he's the only royal who was able to maintain his sentience like Dainsleif and Halfdan? If he stayed in Khaenri'ah he might have succumbed to the curse's full effects but in Mondstadt maybe he could escape it. Anyway we'll need more information before we can confirm or deny any of this.
We also now know that the Homeland brought up all the way back in Mondstadt was really just Khaenri'ah. No I highly doubt the twins are suddenly just Khaenrians. They don't have the right eyes and their clothing looks nothing like Halfdan's. But our sibling seems determined to side with them and "right the wrongs" that befell them. They may not have even learned about what really happened and are just so blinded by revenge that they don't realize Rhinedottir was the reason for all this.
Our sibling's behavior also makes it unlikely that they are from Project A.R.K. from Honkai. The priority for personnel on that mission would have been to find a safe planet to establish survivors from the Previous Era. Fighting against "destiny" is not really going to fit with that mission objective. On top of that the people that were part of that Project would be among the ranks of the Fire Moths meaning they would behave like Fu Hua and World Serpent. (this part will make more sense to people who played Honkai) That would mean that the medieval technology of Teyvat would feel ancient to them but they seem to be right at home.
In my more recent theory I talked about an overarching plot in the Honkaiverse: The rivalry between the Sea of Quanta and the Imaginary Tree. From my big theory (even though it was just me having fun by that point) I think our siblings are what they say they are Travelers that have gone between worlds. In other words they are some kind of beings that can travel to each of the leaves on the tree and that should free them to cameo in other MiHoYo properties in the future.
Anyway going back to Halfdan did you guy's know his name literally means Half Dane? He served under Dain so being "half" sounds a little cute. But no it's Dane not Dain meaning Half-Danish. O well. 
Actually it still opens up a new topic. Most of us know that Dainsleif is the name of a sword but the name itself actually means dead legacy. Dainn is a dwarf or stag in nordic mythology that means "the dead one" and leif is legacy. So I think that's what was taken from the lore instead of being a sword. (Remember my comment on Archons and Gnosis from my big theory.) Because he is literally a representative of the dead legacy of Khaenri'ah which he intends to keep dead.
On top of that I think this quest had confirmed for us that Khaenri'ah is based on the vikings. But not just Khaenri'ah. Sal Vindagnyr is also nordic. Dvalin is another dwarf/stag like Dainn. Irminsul is a pillar in nordic mythology. And the clothing we see Halfdan wear looks close to the French Normans who are vikings.
In another of my theories I pointed out how the time periods of all these nations overlap. The Greco-Roman united civilization actually seeps into both Khaenri'ah's Viking Age and the modern Seven Nations age. That could be a shoutout to Byzantine which for the longest time believed they were the successors to Rome. (because all of them did lol) But at least for Byzantine it was actually a piece of the old Rome (the eastern side) that just became more Greek and then Middle Eastern as time went on and its territory shrunk.
Anyway Byzantine lasted up to 1453 which is right in the middle of the Medieval period and would have included the whole Viking Age too. It is long gone now which makes sense because if we're talking French Revolution Fontaine, 1800s Germany with Mondstadt's Church, Russian Revolution Snezhnaya, Meiji Restoration Inazuma and Wuxia Liyue those all take place long after Byzantine's fall and the Viking Age.
One last thing I noticed about this quest is that Dainsleif said the counter-curse water fountain thing would cause pain to anybody affected by the curse. But what we actually saw were the dying hilichurls, Dainsleif himself and his Black Serpent Knights suffering but the Lector was doing just fine. Why is that?
We know for sure that the Abyss are cursed too. That's the whole point of them wanting revenge. But it is also sure that the Lector and the other enemies we fought weren't affected anywhere close to Dainsleif and the others. So why weren't they writhing in pain too?
It's the quest that keeps on giving. It is likely the Abyss forces were using the "drug" of Abyssal power to numb the pain they were feeling. In other words they were just as much in pain but just like the highly addictive drug opium using it is a very effective pain killer. It's just not a habit to be getting into because of all the side effects and withdrawal. You guys know my theory. Definitely not a good thing to be inhaling lol.
Ok wait 1 last thing.
It'll be great to expand on these but I'll save that for next time! 
Tips and Tricks from a Super Casual Genshin f2p
