Similarities between pgr and wuwa lore
The first appearance of the Tethys System is unknown, it may have emerged out of nowhere just like the Hetero Tower.
The Tethys System performs simulations and predicts future laments.
The Hetero Tower can show various worldlines from different universes and can change the past. Maybe we can do that with Tethys too?
The Shorekeeper is the "key" to unlocking the "gate." In WuWa, the Shorekeeper fills the role of Lucia (possibly the "canon wife" from Lost Memories?), Chaos (the Commandant’s child in PGR), Agent Zero (Rover also shares similarities with this entity).
The Tethys System uses trapped frequencies from the Lament to fuel its calculations similar to the Red Tide, which evolves by absorbing data from dissolved constructs and humans.
My thoughts-
The reason for being chosen by the Tethys system as a key is quite simple, you just need to have a stable frequency. Tethys system chose us as the last resort to become the core computational unit This is where the theory of shorekeeper being our child comes in, similar to creation of Chaos. In pgr you can only enter the hetero tower if you either have the key created by Dominik, you are agent zero, or a hetero creature these three methods work "100%". So key is of importance in both the games.
Solaris-3 has a less hostile filtering process as compared to pgr as people are able to coexist with the tacet discords, or perhaps we(Rover) have already dealt with the dangerous parts of it. Just like how gestalt(a super computer) had trapped agent zero(a dangerous part of punishing virus), which rendered the virus outside forgetting its goal, and also, after escaping, agent zero was fucked by gestalt, which gave it emotions.
The Lucia Looking entity in wuwa could be an Observer (high-dimensional entity) just like Ishmael in pgr.
Rover is from another universe or a singularity, just like commandant or Nanami, who was sent beyond the gate with her starship.
Here is some info about what a gate is (info from ch 31 and ch 32, stage 25 and 22 by Vonnegut and Nanami).
Hetero Tower serves as a shortcut to a gate behind which exists a civilization without life. It's recycling what it deems valuable from civilizations that have mastered zero-point energy and testing them. Those civilizations whose development is deemed unbalanced or incorrect have their data harvested and brought back through the "Gate," where they're left to evolve on their own. (As mentioned above, Nanami from another universe is beyond that gate.)
Why would the "Gate" do this?
To preserve the data seeds of civilization. The "Gate" seeks to carry these seeds through the catastrophe of the heat death, allowing them to be reborn when the universe starts anew.
In pgr it is also said that any civilization which decides to master the zero point energy goes through the filtering process. This could mean that wuwa has already gone through this. I think the Court of Savantage knows and rover also worked with them before as said in 1.1 We just have to find them.
Shorekeeper mentions us being trapped in a mobius loop, which could mean appearing and disappearing across time. Exactly the same as what we do inside the hetero tower. And Tethys system seems like the only place where we could do this. This is just me thinking I could have probably misunderstood or forgotten some of the lore.