Hōrai as a Feywild/Good Kingdom region
by Marc SaindonThis is me recycling the idea of a Feywild retcon into Mystara, which isn't hard to do. In this case, it's loosely based on the idea of Hōrai, which has several versions: "Hōrai is also called Shinkiro, which signifies Mirage—the Vision of the Intangible". So I'll make it a Faerie land, although faeries would be called Yōkai. You might check the Bestiaries for appropriate creatures as Yokai, or re-skin existing ones to a more appropriate japanese theme and esthetic. The animated movie Spirited Away provides more inspiration, and I'm sure there's a way to have Mystaran Totoros as well. Placing them in their own Demiplane keeps Yasuko proper more "grounded" - as far as Space Cat Jungle Japan can go. So the more over-the-top anime high fantasy type of stories could be set in the Shinkiro World, and the (more or less) low fantasy stories happen in Yasuko. The wall between both worlds would be more pourous tell elsewhere, so encountering a Tanuki trickster would not be unexpected in the mundane setting, especially at liminal times (dawn, sunsets) or places (e.g., the beach, which is neither land or sea).
Overseeing the region would be a council of Dragons (use the Shen Lung variant), but they should have their own court systems, with the elements being Earth, Water, Fire, Wind and Void -- distinct from the Chinese version which includes Metal and Wood. You might tie these Elements with the Spheres (e.g. Void being both Entropy and the absence of it since there's nothing left to decay - and spacefaring Rakastas are familiar with the Void of space). I've integrated the proposed that the Shen Lung are a variant evolution of fae Drakes and not Dragon propers (which would also set them outside the influence of the Dragon Immortals).
"Mirror Events" are important in the sub-setting, with a force of nature like a tsunami or typhoon in Yasuko would manifest as Kaiju in Hōrai, something the PCs could team up against and defeat, although such "Gojiras" could only be sent back to the sea at 0 Hit points, where they'll go dormant for a few years.
Notes:
Mount Penglai
Yōkai
Godai (Japanese philosophy)
(Image from: https://www.deviantart.com/jolyonyates/art/Great-Yokai-War-924579017)