The Yōkai Realm is a bizarre yet fascinating alternate universe which was first introduced in Oni Quest - it is home to the spirits known as Yōkai, which have become immortalized in the legends and mythology of many Far Eastern cultures, especially Japan.
The Yōkai Realm can be accessed via special portals across the world, usually in remote areas, though some Yōkai spirits can create their own portals to the Yōkai Realm, which often resemble traditional sliding-doors.
Within the Yōkai Realm reality is no longer run by the normal laws of physics and everything resembles a stylized version of Ancient Japan - yet the Yōkai who inhabit it act in ways that are alien, sometimes frightening, to non-Yōkai.
The Yōkai Realm is rarely visited by humans but often parodies their lifestyle and habits, with many Yōkai embodying certain taboos, obsessions or human flaw - as well as a great many Yōkai who seem to mimic or mock the natural world, such as plants and animals.
Due to the alien nature of the Yōkai which inhabit it the Yōkai Realm is not considered a safe environment for mortal life due to the lack of a normal set of physics - which can result in surreal and disturbing phenomena that while harmless to Yōkai spirits can be frightening and even harmful to humans.