The Dangai was originally both a penal colony and a passage to the
Human World. The Kōryū (拘流, Wresting Flow) and the Kōtotsu
(拘突, Wresting-Surge) are remnants of its time as a penal colony,
they also act as means of defence against unwanted intruders. The
Dangai is an isolated space which is surrounded by numerous stacked-up
layers of time's current, resulting in it being a place where the
density of time within it is extremely high when compared to other
exterior dimensions. To be precise it is over 2,000 times denser,
meaning that when one hour passes in outside worlds, an equivalent of
2,000 hours pass inside the Dangai. The Kōtotsu exists to stop anyone
from lingering in the Dangai and possibly exploiting this time
distortion.
