a large hole opened in the centre of Japan. It was called "The Hell Gate". At the same time as the appearance of the Hell Gate, due to a great natural disaster, the ground shifted, the seas created new paths, and Japan lost it's shape as an archipelago.
There are so many demons in there
Hell Gate will vanish in few years later however it will move to another location.
It revealed The Hell Gate vanished in Japan in few year ago in the ending of Big Bang Age and it appeared up again in Europe
(Note: The name in the translation seems to be "Hell Hole")