I think I've put together a semi-decent theory of what Marisbury's ultimate plan was/is, though my conclusion is entirely conjecture.
Looking at the individual parts of Marisbury's grand scheme, there's CHALDEAS, the Fantasy Trees, the Alien Priestess, and the Animusphere chant.
CHALDEAS we know is a copy of Earth's soul and can simulate the future. It's the Animusphere Mystic Code and uses the celestial sphere model to observe Earth from the void. Earth's texture is currently there, though we don't know what's happened to it since the swap occurred. Using the shape of the cosmos, it can precisely observe the universe.
The Fantasy Trees are almost certainly Animusphere magecraft, and I suspect it's from the Age of Gods since they only appeared in Part 2. The environment of CHALDEAS may have been sufficient to reproduce that original magecraft, though it's impossible to say at the moment if they were the ultimate expression of Animusphere magecraft or if there's still yet a higher level Marisbury intended to reach. Having the shape of galaxies within allows them to anchor Lostbelt textures, and as we know from Daybit and Marisbury's conversation, the shape is enough to observe precisely. In addition to that, they are also "furthest ends", acting akin to Rhongomyniad and fastening the texture to Earth. If the shape is what allows them to anchor textures, then by association observing the shape = being a "furthest end."
The Alien Priestess, let's just dive in and assume she's Olga's soul and (Arche)type-CHALDEAS. She is an observer, and Wodime calls her the void. Her association with observation is noted so often that it's clearly important. Being the brain of CHALDEAS makes her essentially one and the same, the true Alien God. The soul part, I think, is also important, but I'll get to that. But her (and CHALDEAS) being an observer would also make them "furthest ends" and allow them to anchor textures. Sure, Earth's texture is in CHALDEAS, but that can't be the end goal. Well, probably not.
Lastly, the Animusphere chant. Shape is mentioned enough times that we don't need to elaborate on that. The shape is enough. But I'm going to try and decipher the last three, and arguably most important, lines in a way that'll point to my conclusion.
Antrum
The Celestial is the Hollow
Unbirth
The Hollow is the Void
Anima, Animusphere
In the Void, there is God
It's very easy and probably not incorrect to associate this with CHALDEAS, because after all, CHALDEAS is observing Earth from the void, and CHALDEAS/U-chan is the Alien God. But I think there's more to it than that. "Hollow" is a critical keyword here and has been discussed quite a bit. Celestial bodies are hollow (Antrum). But, and this is not just English, it's the Hollow. Antrum is a noun meaning "cavity" or "hollow", also "tomb". The Celestial doesn't need much explaining, but I'd like to point out how Arc's profile refers to Altrouge as a being that "forms the celestial." We briefly talked about the Celestial Egg and the Planet's records in this thread a while back, and a key attribute of an Archetype is having access to those records. Cutting to the chase, I believe the Hollow is the Inner Sea of the Planet.
The Planet (Gaia) is the Inner Sea
The Inner Sea is the Void
In the Void, there is God
The next part is perhaps a little bit of a head-scratcher, not least because of "Unbirth." Unbirth means something that couldn't be born. At least prior to vore becoming a thing. But I want to refer back to Wodime calling the Alien Priestess the void in the shape of an observer. It wouldn't be too much of a stretch to say Unbirth is referring to her. She's not really alive. From a different angle though, if you don't assume "the Void" is referring to space or the universe, there are a couple of other interpretations. One takes Kara no Kyoukai and the simple answer is the Root. Not really rocket science to say Marisbury wants to reach the Root, but for now I'm going to make the assumption that's not his only goal. The other takes Imaginary Number Space. The word used for Void here is 虚空, which, perhaps intentionally, could be seen as an abbreviation of 虚数空間, i.e., Imaginary Number Space. Quoting Comun here on translation specifics:
Sakura's 虚, found in my translations as Imaginary and in FGO NA as Void. Officially defined as "
what can possibly exist but doesn't". It's demonstrated through Imaginary Numbers Magecraft (hence the choice of name), which is Sakura using shadows as space pockets for storing things (Grail mud) and doing portal cuts. Then FGO uses this Imaginary Space to cross walls between worlds by having the Shadow Boarder dive into it (board the shadows, if you will) and surface on the other side. Imaginary Scramble also presents the insides of Imaginary Space as an empty space where multiple possibilities co-exist. Check this event for more detailed infodumps.
Void is possibility. Fantasy. The Inner Sea of the Planet is often referred to by its fantastical and conceptual nature. So a few possibilities, and arguably all interrelated. But keeping this in mind, let's just leave "the Void" as-is.
Those who reach the Root could become god because knowledge is power, etc., etc. But again, putting that aside for now. If the Inner Sea is the Void, then God is in the Inner Sea. Certainly, the Age of Gods is alive and well in the Inner Sea. But more than that, the 最果ての塔 CE states Gaia's soul is located in the Inner Sea. Given the importance of records, it wouldn't be a stretch to equate the soul of Gaia with the Celestial Egg, i.e., the Starlog. Quoting Petrikow on the Retroflow scene:
This is a conceptual universe: |
これは概念の宇宙。 |
Domains which the lifeforms on Earth do not recall; |
地球の生命は記憶していない領域。 |
Laws which are yet out of reach from humanity's observations; |
人類の観測では手の届かない法則。 |
The cosmic hollow reaching into the furthest depths; infinite yet most minimal of all. |
無限にして最小の、最奥に至るソラの空洞。 |
There's a lot more to this quote, which I'm sure Petrikow could elaborate on if he feels it relevant, but this is what Shiki sees when he reaches Luminary Arc's heart. I'm going to assume that the Celestial Egg is primarily Earth-related and not the entire universe, because it's located in the Inner Sea and Gaia is not the Root. But it's Root...like? If the Root is all the records of the universe, the Celestial Egg is all the records of Earth. But anyway. The Celestial Egg is described as residing in a cosmic hollow, using the same 空洞 in the Animusphere chant. You can easily interpret it as saying:
Gaia is the Inner Sea
The Inner Sea is a Conceptual Universe
Within the Conceptual Universe is the Celestial Egg
Potential connections between Aoko's Retrogalaxy and the Animusphere plot notwithstanding (I'm not qualified to touch on that lol), that leaves one more element: Anima Animusphere. Animus is a word meaning many things, including "spirit", "life energy", "mind", "soul", whatever. It's not really that important, you can sum it up as "that which animates." Anima, however, is a derived word which very specifically means the spirit or soul, i.e., "that which is animated." Etymology lesson aside, Anima Animusphere means "the soul of Animusphere." The soul of Olga Marie Animusphere. Olga Marie Earthimilate Animusphere.
Tin foil hat on, the ultimate goal (again, no clue what's happening in CHALDEAS right now, so no point trying to figure that out) is to make the Alien Priestess one with the Celestial Egg, i.e., the soul of the Planet. As an observer with the shape of the cosmos, combined with all the records of Earth, she could anchor, in theory, the texture of any Human Order imaginable to the universe.
Or I could be entirely wrong and CHALDEAS really is the endgame.