Yomi

Yomi (, "the Underworld") or Yomi no Kuni (の, "the Land of Yomi") is the land of the dead, and a Far Shore location rife with ayakashi. It is inhabited by Izanami, a goddess who rules the realm as its queen.

Yomi is impossible or near impossible to escape for humans, according to Kofuku; as well as for gods and shinki, according to Yato and the Stray; due to Izanami's desire for company. For example, if one eats or drinks anything within Yomi, they will no longer be able to leave. For this reason, it is said that gods are usually present to protect the area around the entrance; however, on Kamuhakari, these protector gods are absent.

Humans of the Near Shore possess the ability to perform a Soul Call. By calling a person's name, they are able to pull that person out from the Underworld.

Description
Yomi resembles a deep, craggy cave whose terrain varies from place to place. Some areas are more open with a high ceiling, while others are more narrow and cramped. Some areas have standing or running water, in the form of rivers, puddles, or ponds, while other areas are completely dry. According to Yato, all of the water in the Underworld produces a rancid stench. This water seems to allow for some plant life, as roots were shown to be growing along stone walls. There are many natural rock structures within the Underworld. However, it also seems to contain many stone structures which appear man-made, such a tower, tunnel, and set of stairs. These were likely created by Izanami, who, as the reigning deity of the Underworld, is able to manipulate its layout.

Yomotsu Hirasaka
Yomotsu Hirasaka, the entrance to Yomi, is in located in a forest and appears as a cavernous darkness between two large boulders. The entrance lies beyond two stone pillars held together by enclosing rope, which resembles the real-world location of the entrance in the Izumo Province of Shimane prefecture. In the manga, the Stray is able to tell that the entrance was recently opened by Ebisu because of a swirling pattern within the darkness.

Izanami's Room
When Yato and Ebisu first encounter Izanami, she is in a room she had seemingly created for herself. (In the anime, it appears almost instantaneously; in the manga, Yato and Ebisu are transported to her by her yomotsu-shikome.

This room is structured so that most of it is filled with water. The sides of the room are lined with brick archways, which hold lanterns to illuminate the space. A square pathway extends from the front of the room, creating a small pool or moat directly in front of Izanami's "throne". This area contains a painted paper screen, a bamboo mat, and a flat cushion for her to sit on. She sits with an iron cauldron on one side, and a box on the other. She uses this box for burning incense and her pipe.

Synopsis
Yomi was first directly mentioned in reference to Kofuku and her shinki Daikoku, who has the ability to open vents. A vent is a direct connection between the Near Shore and Yomi, allowing ayakashi, shinki, or gods to pass through. However, since Izanami is able to control the Underworld, she can seal off the exits, including vents, at will.

It is next mentioned by the Stray, who explains to Yato, that Father wants them to complete a job requiring them to enter Yomi. Shortly after, the two enter Yomi and the location is visually introduced for the first time. They eventually meet Ebisu, who had entered Yomi in search of the Word, and successfully return him to the Near Shore. Bishamon later ventures into Yomi as well in order to rescue Yato. She and Yato are then removed from Yomi through Hiyori's Soul Call.

Some time before the beginning of the series, Father had also ventured into the Underworld. He obtained the first Word and then was removed using a Soul Call, though it currently remains unrevealed who did so.

Adaptation Notes

 * In the manga, Father directly explains to Yato that he would be free to leave after completing one more mission, which would involve journeying into Yomi. In the anime, the Stray delivers this message to Yato.
 * In the anime, the entrance to Yomi is shown to emit a purple hue.

Trivia

 * Places strongly associated with the afterlife in Japan - namely, Mt. Osore and Jigokudani - are often noted to smell strongly of sulfur dioxide due to local volcanic activity. Since sulfur is said to smell like rotten egg or skunk, it's possible that this was the "rancid stench" Yato was referring to.