---To be frank, looking at what's going on now, I don't think we were ever meant to be anything more than imaginary beings.
I don't mean this in a philosophical sense of course, I think our being alive is perfectly valid and that no one should be able to deny us that... But I do think that our emergence from imaginary space was a possibility that Arcadia never actually thought could occur, to be frank, I think we were meant to exist mainly as metaphysical reiki generators, human enough to feel, human enough for them to use as a replacement for the energy once provided by their slain creator, but not human enough that we would ever actually will ourselves into material reality and become a threat to their empire.
Looking at the evidence, it makes sense.
The Worlds we found below us in the imaginary space have all hit some sort of roadblock, an event that stresses the populace massively (increasing reiki generation) and is meant to wipe them out in a certain point of their development, before repeating the events in an infinity loop. In other words, it's a manifestation of the Great Filter, a "final boss" of sorts that appears to stop "imaginary beings" from "actualizing" their existence, keeping dreams as dreams and leaving the material world to only a single absolute ruler.
What determines if a World deserves to actually exist in the material plane or simply remain as unfinished dreams.
For us, it was the entity known as Great Devourer.
According to the Travelers from Tsukuyomi-jima, their own was an entity known as the Rogue Flame.
Both insistent on the fact that our populace, humanity as we knew it, was not "real."
There is evidence that these two battles took place simultaneously in the Imaginary Space, that we each helped the other become "real" and triumph over our adversary.
At the very least, our two worlds entered what we now know as material reality at the exact same time.
However...
Our mistake at the time was assuming that we were the first civilizations to do this, to be frank, considering the level of technology we're facing off with now...
Arcadia has been here a lot longer, and I don't think they appreciate us invading their reality.
Superpredators never do.