Miezaru

Miezaru (見えざる, "The Unseen"), or as it is more commonly known, Kyōkai (境界, "The Boundary"); is a hidden realm that flows freely past, trough and around the various Spiritual Worlds in existence; subconciously feeding upon their energy in order to support itself. This leads scientists to speculate that it is not only a realm and world on its own, but also something akin to an artifical intelligence - like an all-encompassing beast that leeches life from the worlds in its vicinity ---they also claim however, that it is vital that Miezaru is allowed to exist, as they believe that without this invisible barrier, all the spiritual worlds would crash together and into the realm of the living, unquestionably resulting in an apocalypse.

The most recent research has revealed something troubling though; the Dangai (断界, Parsing World) have been discovered to, rather than to be a separate dimension in and of itself, be merely a region in Miezaru. More specifically, a serie of caverns; believed to lie beneath.. whatever is up above on the surface. It has been attested by the 12th Division that the well-known Garganta allows the users to pass into or trough Miezaru.

Inhabitants
The 12th Division have fervently scryed, researched and analyzed the surface of Miezaru and have found to their shock, delight and horror that it is indeed inhabited by a wide range of creatures. Although, none of them have been sighted, they can only guess which monstrosities that can possibly hail from such a chaothic and alien world such as Miezaru.

Behind the Scenes
Miezaru is created for the purpose of allowing certain new elements to be implemented at a later date.