It's a land of magic, far different from the outside world. It was created in the days of Feudal Japan, so aside from a few things leaking through the barrier, it has remained that way even as the outside world has matured.

It is a safehaven for youkai, a place where they may be themselves without having to fear humans dismissing the supernatural with their science.

Consider it like a wildlife preserve, except instead of lions and tigers, one has oni and tengu.