Oni, Yaoguai, and Demons

History
Oni have been around in their own realm for a very long time, note that the planes of Oblivion are slightly different from their Elder Scrolls counterparts. The planes are only one, just with drastically different regions. Instead there is a realm for similar to the Chinese rendition of hell 地獄. However, it also seems to have similarities to the Mortal Kombats Netherrealm. Onis however, have not had all too much effect on the realm in which the story takes place in. In the Chinese rendition of hell, a specific type of One exist, the Yaoguai and they are similar to Oni and Demons, but unlike their cousins they are truly immortal. Yaoguai will regenerate in Hell no matter how often they are killed, while Demons can be killed forever in any realm with the right weapon, and Oni can be killed forever in the Nether.

Hotspots in Oni population
Nether/Hell

Hotspots in Yaoguai population
Nether/Hell

Swampia (at certain times)

Hotspots in Demon population
Nether/Hell

Cyrodiil (Briefly, Formerly)

Appearance
Oni differ greatly in appearance. One could look like a shinobi but simply have yellow eyes and a black mask, one could be completely beast like and have no human characteristics. Yaoguai are shapeshifters, they have the ability to change their physical shape and in their natural form are typically completely white. White clothes, and white clothes. Demons are black and grey with orange lines on them in true form. Demons can look nearly human with disguises.

Diet
Oni as a species do not need any food other than souls, which in a way is not food in a conventional term. Yaoguai and Demons have no need for any food.

Teleportation
Oni have teleportation powers. This is very limited but they can go over short distances in less than a second. Yaoguai can teleport over great distances, but they can only teleport a few times every day. Demons don't have teleportation powers.

Regeneration
Oni have a heightened regeneration like most other shapeshifters. However, unless an oni is subjected to its weakness they will heal almost instantly. Demons have no regenerative ability. Yaoguai have the same heightened reiterative powers as Oni.

Inherent Magic Talent
Oni always have talent when it comes to dark magic. Oni also have some power over elemental magic, since some areas of the nether are lava filled and some areas are completely frozen and bleak. Demons have the greatest magic talent.

Nether (Oni)
Oni can only leave the nether if they are summoned or if they happen across a portal. Unfortunately most of the portals have been destroyed and the last ones constantly change place.

Silver (Oni)
Oni are weak to silver, more weak to it than a werewolf. Oni will be immediately dispelled or killed by silver.

Limited Numbers (Oni, Demons, and Yaoguai)
Only 9 Oni can be present at a time.

Frost (Demons)
Demons are instantly killed by frost.

Holy Weapons (Demons)
Holy Weapons can kill a Demon forever, whereas Frost and Ice will only temporarily kill Demons.

Swampian Magic (Yaoguai)
Swampian Magic can pinpoint exactly where a Yaoguai is. Demons and Oni are immune to these spells.

Limited Numbers (Yaoguai)
Yaoguai, despite being powerful, usually don't enter into battles. Yaoguai may be truly immortal but it takes time for them to be restored to a physical form. The only way to kill a Yaoguai forever, is to kill all of them before they have the chance to return. But that is virtually impossible.

Known Oni
Riku Yukimura

Known Demons
Magnus Bane

Sebastien

Morgana

Known Yaoguai
No Yaoguai have appeared