Dangai

The, also known as the Dangai Precipice World, is the dimension between Soul Society and the Human World, seperated from space and time.

Overview
The Dangai appears to be filled with bones and has both the and the  as a means of defense against unwanted intruders. The Dangai is cut-off from both the Living World and Soul Society in terms of time and space. The Koutotsu exists to stop anyone from lingering in the Dangai.

Kōryū
is the current that is constantly flowing through the Dangai, in order to prevent enemies such as Hollows from using it. The current stops souls from moving, and even one foot caught by it makes escape almost impossible. It encompasses the walls, capturing anyone who makes contact with them. Attempting to traverse the Dangai, Uryū Ishida and Ichigo Kurosaki (attempting to save Uryū using his Zangetsu) were almost captured by the current. Luckily only his cape was caught, and Chad was able to break him free. Upon their escape to Soul Society, Orihime Inoue used her Santen Kesshun to block the Koutotsu, composed of the kouryū, and escape, but Yoruichi Shihōin berated her for this action; while the Kouryū only touched the shield area of her ability, had any one of Orihime's Shun Shun Rikka been touched by the current, the entire group would have been killed. If a Shinigami's Zanpakutō is used or revealed, they are also trapped by the current.

Kōtotsu
The, is the Dangai equivalent to a street sweeper. The Kōtotsu appears once every seven days to cleanse the area--killing anyone and everything that makes contact with it--to assure that no one can loiter and take advantage of the time distortion. It looks like the same material making up the Precipice World, only molded into the shape of a bullet train, and a golden eye at the upper-center of its body. If the Kōtotsu touches a Zanpakutō or other spiritual weapon, the user and weapon are trapped, since the Kōtotsu's body is flowing with the Kōryū current.

Shinigami are not supposed to be able to harm the Kōtotsu but Shūsuke Amagai using his Bakkōtō and Sōsuke Aizen in his Hōgyoku fused form have been able to destroy it.

Being chased by the Kōtotsu has shown to lead to time distortion. Ichigo trained for 10 days in the living world, waited 7 days for the Senkaimon, and spent 5 days total afterward, before his 3-Day Bankai training. Logically speaking, this is a total of 25 days, which is exactly (at the time) one day before Rukia's execution after Ichigo's training is complete. However, as luck would have it after being chased by the Kōtotsu, Yoruichi and the Ryoka entered a twisted time-space tunnel when they escaped the Dangai, making their actual arrival to Soul Society about 7 days earlier. This was stated by Yoruichi in her thoughts on the first day of training, so this left a total of 2 days training left, and 8 days following the training that could possibly be used as an extension.

In addition, when Aizen destroyed the Kōtotsu, Ichimaru commented that led to the axis slipping and resulted in them arriving in Soul Society a little further off from Karakura Town.

Plot Involvement
It was first used in order for Ichigo Kurosaki and his friends to invade Soul Society, through Urahara's Senkaimon. It later features again when Orihime uses it to cross back to the Living World with her two Shinigami escorts but is intercepted by Ulquiorra Cifer. The Dangai's deferences were turned off at the time. Later, Isshin opts to use the absence of the Koutotsu to their advantage by using the Dangai to teach Ichigo the Final Getsuga Tensho.

The Dangai and its Koutotsu also featured in The Kasumiōji Crisis. The 3rd Division was sent there to kill a group of Menos Gillian and the then Captain of the 3rd, Shūsuke Amagai, used his Bakkōtō to protect his men by destroying the Kōtotsu, thus winning the trust of the initially hostile 3rd Division.

Appearance In other Media
The Dangai Precipice World was an integral plot-device for the first Bleach feature length film, Bleach: Memories of Nobody. It inadvertently spawned the Valley of Screams, and was revealed to play a role in the creation of Blanks.