Underworld

The Underworld is one of the three realms alongside the human world and Limbo, and is the realm where demons originate from.

Environment
There seems to be no signs of weather in this realm other than the permanent thunderclouds in its atmosphere and tornadoes. The geological features of this realm are plain, with nothing geologically significant other than mountains made of blueish-green minerals. Water and plants do exist in this realm, as evident of Jack's village. The heat in this realm are given off by the geothermal heating underground, as evident when Shi Ji attempted to steal Yan Wen's Heaven Crystal fragment by sabotaging the geothermal heating and causing an explosion.

History
The Underworld is the ancestral homeland of demons, as well as where some of them retreated to after a secret truce was established between Yan Wen, the ruler of the Underworld, and Wang Shengli, the secretary of the Department of Night that prohibited monsters from terrorizing humans. It was once conquered by Xi Sha's previous incarnation before she died and the position was somehow succeeded by Yan Wen.

Individual demons
Yan Wen: Ruler of the Underworld. Most of the Underworld is under her control. Very few races of demons aren't governed by her.

Left-hand Man: One of the two assistants to Yan Sis.

Right-hand Man: One of the two assistants to Yan Sis.

Jack: A member of the Transmit Demons and lover of Rose.

Rose: A member of the Transmit Demons and lover of Jack.

Y'Shari: Former co-ruler of the Underworld along with Xi Sha's previous incarnation, and King of Qin'guang Valley.

Y'Shari's follower: An elderly demon who was sealed away along with Y'Shari. He can shapeshift.

Demon races
Four Imperial Guard Clans: Four races of demons that serve under and protect Yan Sis. Consists of the Power King Clan, the Iron Hoof Clan, the Sky Slash Clan and the Elder Clan. The younger generation of these clans were all killed within the Limbo Stone dimension created by Shi Ji.

Luoying Clan: A race of demons that are natural-born spies. Conducted multiple espionages during the Warring Period in the human world.

Luoren Clan: A race of demons that are natural-born assassins. Conducted multiple assassinations during the Warring Period in the human world.

Transmit Clan: A race of demons that are born with the unique ability "Telepathy Link".

Locations
Blood Pool (血池): A pool of blood that nurtured the souls of the two demon lords after they were killed and eventually reincarnated them. It is located directly in front of Yan Sis's throne.

Jack's village: A village of straw huts where Transmit Demons reside.

Sealing Grounds (封印之地): The Sealing Grounds is an area in the Underworld that holds a demonic three-headed stone statue. Y'Shari and his servant were sealed within this statue by Yan Wen for almost two hundred years.

Chaos Hunting Arena (混沌猎场): A hunting grounds made for demons to indulge in their bloodlust and hone their battle skills. Despite its chaotic state, there are many rules within the hunting grounds enforced by its participants.