A long while ago I guessed at a possible plot for Fischl. At first it was just a fun idea but there's more information that lines up with that fun idea now.
More recently I came up with the idea that Oz is pushing Fischl in the direction of being the Prinzessin instead of living her human life because he's actually Naberius another Archon.
That newer theory came from looking at the Legend of the Shattered Halberd and Flowers for Princess Fischl books. I know there've been many interpretations of it already but I don't think anybody came up with this yet.
So the first thing is to know that Legend of the Shattered Halberd is just fiction. There are theories on who Mr. Nine is but I think we haven't met him yet and that'll be important too. The other volumes do build into my theory but only because they explain the specific characters and descriptions of Vol. 6. (Also when I say that I mean the Chinese words being used. The English version is just mad. 
)
I think Vol. 6 is the only relevant piece of information we can take from this series. Mr. Nine wrote this one much later than the rest of the series, he did it not really on his own either and he even admits it plays off of his newer series Flowers for Princess Fischl.
And you guys might be sick of me bringing her up but the reason why I think Vol. 6 is the only important part is because Yae's the reason why Mr. Nine wrote it and we know fans of his series noticed how different it read compared to the rest of the series too. It's really funny that they specifically included Yae saying "I didn't pressure him into writing it this way. It was all him. Totes honest!" You know who I think Yae is so there is no way she'd be involved and come up with this obvious hint that she's telling us what's really going on if it didn't have a purpose. 
So what are we supposed to see here? Again you have to at least cross-reference from the original Chinese for any of this to make sense. The spirit possessing Weiyang is actually "Fischl" and she's the daughter of the "God King" "Celestial Emperor" who appointed her with the task of piercing him and reconnecting the nine realms. We have not heard anything else about the nine realms but we do know something else. Irminsul is what we call the Ley Line trees all over Teyvat. The "first Divine Halberd" was supposedly something that connected all of them. (Genshin's version of the nine realms and Yggdrasil) So Fischl is supposed to reconnect those Ley Lines back together.
From the fact that Yae manipulated Vol. 6 to tell us that information and that the Abyss were after a book that talks about the Night Mother who is supposed to renew the world I think both factions are working on the same thing but for very different reasons.
You see the Abyss is after revenge against Celestia and I think one of their many schemes will be making use of Fischl to do it based on the fact that she's supposed to fix the world by "piercing the God King" and "swallowing all dreams" to bring in the new one. But from Vol. 6 and Flowers we're getting Yae's version of it which is more about reconnecting the broken Ley Lines after Celestia's attacks on the Archons and its destruction of Ley Line trees like the Frostbearing Tree.
Last time I said that Oz might be getting blackmailed by Rhinedottir who has his heart. This heart could return Oz back to his true self Naberius. But in Flowers we learn that Oz/Naberius might be in love with Fischl. So for all the drama points maybe their previous Archon forms the Night Mother Amy and the Night Raven Naberius were together something like Zhongli and Guizhong. When Phanes descended and started killing the Archons both of them were diminished with Oz losing his strength and physical form while Amy was turned into a human with no solid memory of who she really was.
"Find meaning somewhere. The night deepens, but the dream lives on."
This is a quote from Fischl's "mother." Taking it directly just sounds like something cool to tell a main character. But if Amy was really Amy from the Ars Goetia then the fact that she lives means the dream can live on even while the night deepens. (Teyvat's a mess right now.) She just needs to find that out.
So in Flowers and Fischl's teaser theme we get another term Sommernachtgarten. This means Summer Night Garden and is actually the Midsummer Courtyard where we farm for the Electro Artifacts. This is also the Ascension Domain. In Flowers this place is supposed to store everyone's emotions and experiences so this could be the where she finds "meaning" aka who she really is. But wait there's more.
Most of the stories we know about Fischl are about the end of the world. Some people have already noticed this but Immernachtreich is just a word using German to talk about Tokoyo no Kuni. The confusing part I'm noticing though is when to use real world lore and when to use Genshin lore. You see Tokoyo no Kuni or Tokoyokoku is one of many ways to say Enkanomiya in Genshin. But from my topic on that Enkanomiya was just based on the legends about Tokoyo no Kuni an Okinawan underworld. In Fischl's case Immernachtreich is the underworld reference itself. From the stories the idea is that Fischl is the ruler of this underworld and everything will be dragged by entropy back into it to be reborn into a new world.
And we can see that this is the case because the Chinese for Immernachtreich is not the same thing as if you translated it from German. 幽夜净土 is the term and it might interest you guys to know something about this. The last 2 words here 净土 are also found in another term 一心净土 the Chinese name for Ei's Plane of Euthymia.
So what does that mean? Well Ei's an Archon right? If she can create a plane for herself based on what she wants out of it (一心 means single-minded resolution, the whole thing means a single-minded resolution to remove all desires aka ambitions) then so can the Archon Amy. And her plane might be a Land of Night.
Now if we put all that together it all goes back to how she's supposed to renew the world. As the Archon Amy she can create a plane called the Immernachtreich which will draw everything in. And then she burns away her heart to renew the world. What's this about? Well Midsummer Courtyard has a Ley Line Disorder all related to Pyro Visions doesn't it? And Fischl only has so many friends. You've got the Traveler and Paimon, Oz and you've got Bennett. In my first theory I said Bennett might be how Fischl frees herself from the Night Mother/Archon side of herself so that she can finally write her story hinted at in her Story 5. And we just so happen to have a heart for ol' Benny boy to burn. The Heart of Naberius. What if Oz is letting Rhinedottir blackmail him with his heart so he can bring Amy back to her full power only for her to be able to throw away the pain of the old world (her life as an Archon) and move on into the new world? (just being Amy) And to allow that to happen he wants Bennett to burn away his heart when the time comes.
That'll leave him permanently as Oz but that could be how that story will end. Fischl now comfortable calling herself Amy will be a normal allogene again with her Electro Vision which was all that was left of her Archon powers following the Abyss operation. Meanwhile the power that made her the Night Mother will fulfill its purpose. Similar to Guoba after Bennett frees Amy by burning the heart all that Archon power floods through Teyvat and reconnects the Ley Lines by releasing all of the stored experiences it had collected from the Midsummer Courtyard.
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The rest of this is just additional details I thought were interesting but didn't really fit into how I wanted to present the theory.
If you read the lore for Fischl's bow the Mitternachts Waltz it pretty much says that she comes from a time in Teyvat's history when the moon sisters ruled and when the Archons began to fight each other. (There's more to it than that but I think that's more Honkai's territory. This weapon was made for the crossover. Funny enough it kinda touched on another topic I made. Reman Republic lol)
Anyway Mitternachts means midnight in German. This weapon in Chinese is 幽夜华尔兹 where 华尔兹 is a transliteration of Waltz so we're left with 幽夜 Immernachtreich. The English localization inconsistency strikes again lol
There's a video game like segment in Flowers. Apparently Fischl is only at a power level of 10 but Oz being a "Beast of the World" is a 13. If you look at the Ars Goetia if Oz is Naberius and Fischl is Amy then Oz outranks her. Of course in my theory the ranking has nothing to do with power level but it's still funny to think about.
In Flowers there's also a Yae thing at the end. One part is a fan question asking how the "Asura Khan" from Legend compared to Gesamtkunstwerk in Flowers.
Well:
1. Asura Khan is actually what they call it even in the Chinese. I'm not sure why they combined Mongol and Indian culture but I think the point is the Asura part. The full name from Legend is Asura Khan of Jotunheim. (In English they wrote Khan the Asura like Khan's a name. It isn't lol) Jotunheim is the Norse land of the frost giants and Asura are comparable to titans. Remember what I said about Oz last time? He's related to Norse Ymir the frost giant that Odin kills to make the world from his body.
2. Asura Khan wields a weapon called Laevatain. This is actually Loki's spear that's said to always strike its target. So likely another Divine Halberd. Asura uses it to defeat Fischl and Fischl says that the world is destroyed again as the spear burns everything. (Asura are also related to fire.) You could probably look at it like a bad ending if Fischl's not the one to do the burning.
3. Gesamtkunstwerk is shockingly a word ported to English which I have no idea how you'd pronounce it in English lol. It means masterpiece so I guess like a perfect monster. But here's the thing. In Chinese Mr. Nine doesn't say "my Mora's on it being stronger." He just says he did a coin flip and Gesamtkunstwerk won so his answer is much less convincing.
And one last thing about Flowers. That's not the original title. In Chinese it's both simple and cute. So it's 菲谢尔皇女夜谭 where 菲谢尔皇女 literally just means Princess Fischl. On the other hand 夜谭 could simply mean bedtime stories so like Fischl's Bedtime Stories. BUT 夜谭 comes from this phrase in Chinese 天方夜谭 which is from 1001 Arabian Nights. (yeah this part is totally not related to this theory I just thought it was cute) If you don't know this story basically there's a princess that kept telling the king a new story every night or he'd kill her. After 1001 nights of stories the king ended up falling for her and married her so she saved her life by telling just a ton of stories lol. And that's what 天方夜谭 means, the ability to tell all kinds of stories. 
Wait ok one last thing (that last one didn't count!) so Flowers for Princess Fischl. I think this might have come from a real story called Flowers for Algernon. And I think the localization team were being funny when they came up with it. Flowers for Algernon is a short story about a dumb guy who gets an operation that makes him super smart. But because he becomes smart everybody around him can't get used to it and he ends up alone. Then he finds out his new intelligence is also temporary so when he becomes dumb again everybody pities him and he can't take it so he runs away. Really sad. Anyway the first part of it feels like Fischl's whole chuni thing and that's probably where the localization team got the idea. But if my theory is right she will end up going through "an operation" that makes her honestly as powerful as her chuni thing makes her believe only to lose it again. Hopefully it ends better for her than it did in the short story.
Did everybody make it to the end ok? 
Tips and Tricks from a Super Casual Genshin f2p
