Demon Gate

The Demon Gates or Dark World Gates connect the Human World to the Dark World.

The gates are constantly active and open, leading to Demons entering the human world. However, are hidden and not easily accessible.

History
Though gates existed in some form in the long past, most became inactive. Only as recently as the Peninsula Conflict did multiple of them show up around Japan. After a large explosion in Amidahara, a small number of large and multiple small portals opened around Japan.

It is currently unknown what opened the gates but one possibility is the UFS did it unintentionally as they also researched other dimensions and the Otherworld.

When a demon gate is found, the demons and outlaws settle to bring massive profits. Currently closing the gates seems not to be possible and the largest gates are located in Yomihara under Japan and in Amidahara.

Trivia

 * Unlike the gates to the Otherworld, gateways to the Dark World are more stable. However, Miasma of the Dark World did affect the areas around the towns, they are found in.
 * How the gates really look has not been shown yet.
 * The gates were first mentioned in Witch of Steel Annerose.