Yomi Wan

Yomi Wan, also called the Thousand Hells is an artificial reality created (or stolen) by the Yama Kings to serve as their bolthole and headquarters.

Location
Originally, Yomi Wan was simply the private domains of the Yama Kings; at the beginning of time, the Yama Kings were purifiers and redeemers, necessary jailors who obeyed the August Personage in Jade. As such, they had their own pocket dimensions where they enacted their necessary, if unpleasant, duties.

As the Yama Kings fell into corruption, they carved spiritual lebensraum out of the Ying World and Yang World. These stolen dimensions were crudely welded together by the Yama Kings, resulting in visible scars throughout Yomi Wan.

Nature
Yomi Wan is a crazy-quilt domain; each Yama King claims some space as their own personal Hell. Most hells are Yin or Yang aspected, a function of their Yama King and original territory, but there are visible scars throughout the realms - unstable fluxes in reality that occasionally move, wreaking havoc everywhere they go. The Yama Kings war over territory on a regular basis, usually by claiming each others domains for their own. As a result, Yomi Wan is unstable and in a perpetual state of flux.

The domains of each Yama King differ widely but are connected in some fashion, one could theoretically walk from Kakuri to the Wicked City, however the active interest (and knives) of the Yama Kings prevents this from happening easily. Similarly, there are passages to the Yin and Yang Worlds, but traversing them is insanely difficult.

The major activity in Yomi Wan is torture, andthe extraction of Chi from individuals suffering extreme pain. As a result, sinners are everywhere in Yomi Wan, as are horrific and painful things happening to said sinners. The Yama Kings are firm believers in advancing the craft of pain, and have found exciting new uses for rubber tubing and dentral drills. Almost everyone in Yomi Wan is a sinner, Akuma, Demon or Yama King. Anyone else is likely to find themselves in the torture chambers pretty quickly.

No matter how horrible the Thousand Hells are for the sinners, they are ever so slightly worse for their ostensible jailors. Despite everything they have done, there is something not quite "right" (as far as Yama Kings are concerned) about Yomi Wan, righteous individuals like Jizo wander throughout Kakuri Hell with immunity, souls escape. Things mess up in the most ironically redeeming of ways. These events are not common, but they are visible and well known enough to make the Yama Kings wonder if when the August Personage smiled and turned away, he was the only one who got the joke.

Major Hells

 * Kakuri, controlled by the Yama King Emma-O. Kakuri is a Yin-aspected domain, a lightless, joyless, honorless void of ice and snow.  As an ancestral domain of the Ainu, Kakuri hell has a secret way out for Emma-O's original worshippers.
 * The Wicked City. The domain of Mikaboshi is a nightmare of cyberpunk and anime extremes coupled with demented Feng Shui and management theory that would leave Spencer Johnson curled up in corner driving spikes into his eyes.  Mikaboshi is very proud of his little project, he constantly tweaks everything from power generation to the economics of the systmem, and looks forward to invading the Middle Kingdom with his urban renewal project.
 * The Hell of Burrowing Maggots. Controlled by Rangda, mistress of pestilence.  The Hell of Burrowing Maggots is pretty much what it sounds like.  It's a hell.  It's got Maggots.  Lots of 'em.  All shapes and sizes.  You're lunch.
 * The Hell of Being Skinned Alive. The domain of Tou Mu.  The Hell of Being Skinned Alive is a desert enduring constant winds of fast, fine, lacerating sand.  Unprotected beings are flensed in minutes.  Tou Mu herself rules from a palace in low orbit decorated with the impaled (and living) bodies of those who have annoyed her.
 * The Hell of Boiling Oil. Actually it's fat.  Delicious rendered human fat.