The Ōmagato Empire

The Verge, the Unseen Village, and Aburayan Springs used to be the westernmost, oversea holdings of the Empire.
When doom came for this culture, only the Unseen Village managed to survive, hiding within illusions and isolating itself from the rest of the world – until now.
However, there might still be other living survivors on Eastern Landmass™; enclaves, sects, and similar isolated groups, who also stayed behind instead of fleeing through the Portal. Most likely supported by the Dragons (see below) that also remained, they might have even prospered for some time under the rulership of their Dragon-Kings, until the Empire failed the second time for some reason.
Apart from Kitsune (often the ruling class), Tanuki (usually commoners) and Unknown (most often the middle class), other creatures that existed here – and continue to exist today – are Spirits such as Kami and Oni, as well as Vampires such as Jiang Shi.
The social strata, while present, weren't strictly divided and enforced, and any of the three ancestries could belong to any of the classes. Kitsune farmers or Tanuki nobles weren't that rare of an occurrence.
The language spoken was Ancient Sylvan.
Probably an Asian-derived Unknown or two, such as Sovereign, Sea, and Sky Dragons, Pixiu, etc.
Dinosaurs prowl the jungles, maybe even pterosaur-looking Dragons called Kongamato.

Another culture, which coexisted with Saqqara and Achaeans, used to exist here in the first age of the New World – Eastern Landmass Civilisation.
The Ōmagato Empire inherited some things from them, such as ideas, concepts, culture, etc.