Disclaimer
As per title, the post is a theory containing spoilers about Fontaine Archon Quest act I and II (version 4.0). If you still have to play the quest, I'd advise to come back later.
All the links and sources used in the post:
- "Full Fontaine Archon Quest Act 1 - Genshin Impact 4.0" by Fayato on YouTube
- "The Subterranean Trials of Drake and Serpent" World Quest
- "Three Realms Gateway Offering (The Eve / Part I / II / III / The Aftermath) (Event) (JP VO/ENG Sub)" by Teyvat Travel Guide on YouTube
- "Mondstadt Archon Quest: Full Prologue Gameplay Walkthrough | Genshin Impact" by MaL AnimsGaming on YouTube
- "Overtune Teaser: The Last Feast | Genshin Impact" on YouTube
- "Full Fontaine Archon Quest Act 2 - Genshin Impact 4.0" by Fayato on YouTube
- [2.6 Archon Quest] Chapter II: Act IV - Requiem of the Echoing Depths (Japanese)
- In-game descriptions
This theory can also be found on Reddit
Introduction
It has been a while since Childe has made an appereance in Archon Quests, and he's already causing chaos - unwillingly, this time. From simply helping the Fontaine branch of Northland Bank to collect debts, occasionally sparrying with Champion Duelists, to end up incarcerated because a Weird Machine - Is This How Fontaine Does Justice? Eh? - said he's guilty of a crime he didn't know about until probably five minutes after entering the Opera. I, too, would have tried to take down the court if I were him to be honest.
After playing the Archon Quests, I have some questions regarding the whole "Childe is guilty" ordeal:
- Why is Childe in Fontaine?
- Why is he in a bad mood?
- What happened to his Vision?
- Why did Skirk choose to train Childe? What is "it"?
- Could the whale in Childe's dream be related to the Primordial Sea and the prophecy?
Alright's let's dive in! I'll try my best to motivate my answers in the post; I would love some input/feedback if you want to share ideas in the comments.
One: Why is Childe in Fontaine?
In the new Fontaine Archon Quest, we first meet Childe after talking with Estelle in the Beaumont Workshop and the Confrerie of Cabriere's men's, mainly Truand's, interruption; Childe is asking them to pay their debt to Northland Bank, but soon notices the Traveler and completely ignores the men who, understandably, don't appreciate this treatment.
Childe tells us he has been in Fontaine for a while now, and things are getting a bit boring, to the point seeing the Traveler is enough for him to feel excitement.

"Full Fontaine Archon Quest Act 1 - Genshin Impact 4.0" by Fayato on YouTube
Something I did take notice is how Truand keeps trying to bring back Childe's attention to him and the latter starts to become increasedly more irritated. And, not too long after, when we ask him the real reason why he's in Fontaine, he tells us he's currently in a bad mood, something Paimon so graciously remarked is unlike Childe.

Travel Log
Childe being in Fontaine, at least from what we can gain from him, is for personal reasons: he's looking for something, anything, that could help him fight off the bad mood; that's why, when seeing us, he's happy - because wherever we go, we "always seem to find trouble" (which is ironic, considering the description of his boss in-game - we'll come back to it later).
Two: Why is Childe in a bad mood?

"Full Fontaine Archon Quest Act 1 - Genshin Impact 4.0" by Fayato on YouTube
He's aware there is something in him that is making its presence known, but only started to do it recently - meaning, Childe didn't feel this presence before but, "every now and then", he feels something's wrong. Paimon connects the power to the Vision's sudden malfunction, a theory I do agree with, but I would also connect the mood swings to this same power "stirring" as well (another something we'll come back to later. Oopsie).
Three: What happened to Childe's Vision?
Childe tries to summon his Hydro weapons to finish off Truand, however, he doesn't succeed; then, the light of his Vision dims - but it doesn't turn grey like when a Vision user dies. Sitting in our inventory, after Childe tosses to us his Vision as safekeeping, we can see and read how it lost its glow.

Inventory
Whenever we'll keep it with us permanently or not is uncertain (maybe he'll ask for it later, maybe he'll won't need it anymore, growing past it); as said before, Paimon links the malfunction to the power Childe feels and Traveler connects the power to the abyss Ajax fell in at 14.

Travel Log
The power Childe is feeling can pretty much be abyssal in nature; after coming back from that "land of darkness" (Foul Legacy's boss fight description's reference), Childe's personality changed drastically.

Tartaglia's Profile
In the world of Teyvat, according to the people of Byakuyakoku there are three Realms: the Light Realm, the Human Realm and the Void Realm; from the Light Realm or Vishap Realm, we have elemental beings, from the Void Realm or the Abyss, we have creatures like Rifthounds, Abyss Heralds, Lectors and Abyss Mages. Thanks to Enjou in an Enkanomiya World Quest, we know the Void Realm and Light Realm are opposite to each other.

"The Subterranean Trials of Drake and Serpent" World Quest - Extra dialogue from Enjou
But honestly, we don't have to go that far - we know abyssal powers can corrupt/taint elemental beings since Dvalin's corruption in Mondstadt Archon Quest. The Void Realm hurts both creatures from the Light Realm and Human Realm: Lisa, when closing the distance to Dvalin's corrupted tear said the impurities imbued into the tear hurt her, as her Vision repels the energy into the crystal and viceversa. This, obviously, means Visions and abyssal power have repelling properties to each other, thus they have different Realm origins.
All of this to say - Childe has been tainted by the abyssal power, and now that its presence has been stronger to the point of being acknowledged by its host it is repelling Childe's Vision. I think the taint can be a possibility both for the change of personality and, maybe, for changing Childe's fate to now be the center of every conflict.
The taint and possible change of fate are both mentioned in Childe's boss fight drops.

"Memories: The Golden Shadow" Weekly Domain

"Memories: The Golden Shadow" Weekly Domain
(Note: I do believe Traveler doesn't know Foul Legacy has nothing to do with the Delusion. That's why all of Childe's boss fight drops start with "[...] who has unleashed the might of his Delusion".)
Four: Why did Skirk choose to train Childe? What is "it"?
We have known for a while Skirk was the mysterious swordswoman who taught Childe the Foul Legacy and almost all of his combat abilities, thanks to Childe's Character Profile.
What we didn't know until the new Archon Quest was the reason why she chose to teach him how to survive the Abyss: Ajax awakened "it", and traces of "it" remained in him.

Travel Log
It is interesting how, in Tartaglia's Profile, it's said Ajax falling into the Abyss was likely not an accident: the Realm sensed his ambitions (which is intriguing on itself how this could imply Visions and the Abyss work in similar ways; could the Abyss work on obsessions, instead of ambitions?). It is left vague, probably on purpose to not spoil future content.

Tartaglia's Profile - Character Story 4
Another interesting thing to note is how Skirk, according to Childe, said all of Ajax's training would have become useful in the future. It is likely Skirk knew, upon sensing the "it" remains in Ajax, what the boy's purpose would have been later on and, I think, this also supports the theory Ajax's fate was changed for a new purpose Skirk knew about.
Skirk recited what looks like a prophecy for Tartaglia, that we can read in the Living Beings section of the Archive. We actually don't have confirmation these are Skirk's words, but it wouldn't seem far fetched to assume it is her:
- she was the one to teach Ajax the Foul Legacy; his namecard's description confirms as such
- in Tartaglia's Profile, we can read Skirk taught Ajax both how to survive the Abyss and nurtured his ability to cause storms wherever he goes

In-game Living Beings Archive

Tartaglia's Profile - Character Story 4
Alright, great, but what exactly is "it"? And why is "it" so important now?
Childe tells us "it" might be in someway related to a dream he saw after falling into the Abyss. In the dream, he was in the depths of the sea, when a massime whale appeared and he felt like he couldn't breath for how big it was.

"Full Fontaine Archon Quest Act 1 - Genshin Impact 4.0" by Fayato on YouTube
Childe is often associated to sea creatures ever since his introduction (nope, this is not about Osial, I promise); Tartaglia's constellation is a sea creature or, to be precise, a Celestial Narwhal (Monoceros Caeli for the nerds).
We see the same narwhal replicated by Childe himself in his boss fight and he tells us he took inspiration by the whale in his dream for the devastating attack.

Travel Log
A constellation represents the person's character and fate, like Monoceros Caeli is said to represent Tartaglia in another of Childe's boss fight drops description.

"Memories: The Golden Shadow" Weekly Domain
I do not think this is a coincidence: if Ajax's fate has been really changed, if the Monoceros Caeli constellation and Childe's attack in the Golden House are so similar and the same attack is inspired by the whale Ajax saw in the Abyss (and I would like to point out how the names of the constellation contain words such as "abyssal mayhem" and "havoc"), then perhaps the "it" is indeed related to the massive whale, because the "it" is the whale; and the traces "it" left behind are maybe fragments of the whale's powers, or perhaps fragments of "it"-self (lame joke, I know).
And if "it" is truly the whale Childe dreamt, and we theorized "it" is the power, or entity, repelling Childe's Vision and giving him mood swings, then the whale could be an abyssal creature venturing in the deepest parts of the world.
Five: Could the whale in Childe's dream be related to the Primordial Sea and the prophecy?
Coincidentially (well... not?), Freminet appears to have had the same dream in the Fontaine Teaser: we see him underwater, sinking, when suddenly a massive shadow appears in front of him and he starts to suffocate. This segment of the teaser seems a bit too on the nose to me after playing the Archon Quest.

"Overtune Teaser: The Last Feast | Genshin Impact" on YouTube
The words that open this scene are as follows:
"The original sin is the fairest: everyone sinks... Make the most of the final feast, because for the sinners, the curtain call has come"
The only one we don't see, listed in the description of the video along with the other VAs and characters, is Egeria, heavily hinted to be the previous Hydro Archon.
Anyway, what is important now is the "sin" and the "sinners" she's mentioning: she's telling us time is up, because the "curtain call" is coming. Curtain calls occur at the end of a performance, when all the performers are called on stage to be recognized by the audience and bow: the sinners are in the last moments of their performance... what did Lyney in act I say about the prophecy?
"It says that every person in Fontaine is born with "sin". No matter how the Nation of Justice holds trial after trial, this sin cannot be absolved."
"Until one day, the water levels in Fontaine will rise, and the sinful people will slowly be drowned..."
"In the end, the people will all be dissolved into the waters, and only the Hydro Archon will remain, weeping on her throne... Only then the sins of the people of Fontaine will be washed away"
The people of Fontaine, the "sinners", didn't give much thought to the prophecy, but now the water levels are rising and we discover already in act I people can be dissolved thanks to the Primordial Seawater. Egeria has warned us: the moment to be recognized as sinners by the audience is near - the moment for the prophecy to be true is approaching.
Now, why show what we can now assume is the a massime whale during Egeria's speech, if it's not related to the prophecy in some way?
It is the first time the Primordial Sea is mentioned in an Archon Quest, but the artifacts lore is always one step ahead: in the Nymph's Dream set there are two lines that stood up to me:

Nymph's Constancy

Fell Dragon's Monocle
The lore in the artifact set refers to the Narzissenkreuz - there's a whole World Quest for it. In the first line, there's a "primordial liquid" capable of dissolving all - the owner of the watch was dissolved. Primordial Seawater has the same properties to dissolve life (as we saw in the Archon Quest), but it is also the water were all life comes from - and could have cleansing properties as well, since we're talking about sin and washing away -, according to the Remurian legend in the Dross of Pure Sacred Dewdrop weapon ascension material:
"It is the purest origin of all things, and one day, it will also swallow all life... and those things which did not arise from it will be filtered out, becoming naught but floating detritus."
(Note: Fontaine is the first time we hear the term of this water, but it is possibly not the first time we see a water with the same properties, especially cleansing ones. In the "Requiem of Echoing Depths" Archon Quest, we encounter an upside-down water pool, just like the water we found in the Fontaine Archon Quest is upside-down)
For the second line, well, the amniotic fluid could the Primordial Seawater; but what about the "star-beasts"?
I think, in this case, the star-beasts are abyssal creatures (stars are often associated with the Abyss), and I believe one of these creatures is the whale in the teaser; if that's the case, the massive whale could be somehow responsible of the prophecy, by allowing the Primordial Seawater to flood Fontaine or simply bringing it back - although, during the Archon Quest we found a pool of Primordial Seawater. It is just not enough to flood an entire nation.
This is the point I'm the least confident about, because the "star-beasts" could just be a metaphor for something else; however, I don't think it is a coincidence an "amniotic fluid" is mentioned and, most importantly, I don't think the whale in the teaser and the whale in Childe's dream are simply not one and the same.
The trial and the Oratrice's "guilty" verdict
Here comes the fun part: Tartaglia - ahem, Mr. Tartaglia, apologies - has been charged for the "Serial disappereances of young women" case by... someone. Honestly, from what we've learned about the Court System in Fontaine, Childe's trial doesn't make the tiny least of sense: who accused him of the crime? Why is the Court not allowing Childe to fight? Didn't anyone in that Opera think about the fact Childe was probably a toddler when the disappereances started?
Anyway, the charges quickly fall to a different character, Marcel.
Marcel, or Vacher, in order to bring back his lover who fell accidentaly into a pool of Primordial Seawater and, due to her Fontainian origins, was dissolved, for around 20 years kidnapped young girls to use them as test subjects for his experiments with the water. All the girls were dissolved, causing the serial disappereances.
Neuvillette's verdict is "guilty" and the Oratrice, rightfully so, confirms the "guilty" verdict.
That's it! The 20-years-old case is solved, everyone can go home! Surely there won't be any unexpected twist-


"Full Fontaine Archon Quest Act 2 - Genshin Impact 4.0" by Fayato on YouTube
Is the Oratrice malfunctioning, or is Tartaglia declared guilty out of principle, because he's a Fatui Harbinger?
The Oratrice worked just fine earlier and logically, as Neuvillette pointed out, Tartaglia couldn't have possibly been responsible of the crime: all the clues pointed to Vacher and the latter confessed to have, indeed, caused the disappereances. As the members of the audience pointed out, this is the very first time the Oratrice's verdict has been different from the Chief Justice's.
Could the verdict be because he's a Fatui, then? Unlikely: Lyney is also part of the Fatui, but the Oratrice declared him innocent for the "Opera House switcheroo" case.
Neuvillette tells us the people's faith in the concept of justice is integrated into the machine, but in the audience many people were skeptical and confused by the Oratrice's verdict; the Oratrice, then, doesn't simply use the faith in justice for the verdicts, nor it does automatically repeat what Neuvillette says. In fact, the Chief Justice suspects the Oratrice is self-conscious and that's probably why during trials we can see the machine shifting towards one party's favour or the other: it is gathering all the informations in order to give the proper verdict, like Neuvillette does.
So, let's take a step back: what was the charge about?

"Full Fontaine Archon Quest Act 2 - Genshin Impact 4.0" by Fayato on YouTube
Wording is important here: the charges are about the serial disappereances of young women; not murder or kidnapping, but disappereances.
And how was Vacher able to dissolve the young women, what was the murder weapon? The Primordial Seawater.
If we conclude the massive shadow in the teaser behind Freminet, the whale in Childe's dream and the "it" that left traces in Ajax are all the same, if the whale is connected to the prophecy and the Primordial Sea, then the Oratrice's verdict might have sensed that "it" in Tartaglia and declared him "guilty" for the murders, because what ultimately caused the women to "disappear" was the seawater.
Of course, Childe didn't directly kidnap or murder any of those women and learned of the case when he was accused. But if the "it" is "stirring" to the point Childe's mood and Vision are affected, then it's not too far fetched to think the Oratrice, divinely created, has recognized the traces of the entity.
So, the Oratrice is not completely right, but it is not completely wrong either: Tartaglia is innocent. But the "it" inside of him, that he has awakened, is guilty.

