One Realm

"I used this ultimate weapon to warp reality, merging the realms into a singular existence....the Elder Gods were helpless and I used their own power against them, in the Void beyond the One Realm."

- Onaga, in his secret ending for Mortal Kombat: Deception

The One Realm is a non-canon name given to the outcome of merging all the realms into one existence. The only known means of creating the One Realm is through fusing the Kamidogu with the assistance of the Amulet of Shinnok, then saying a special incantation. It is not clearly known whether or not the "minor" realms (realms that are not Earthrealm, Netherrealm, Chaosrealm, Outworld, Orderrealm, or Edenia such as Nightmare Realm, Zaterra, Vaeturnus, etc.) can also be merged into the One Realm, or even if the "minor" realms have their own Kamidogu to start with, although in Onaga's secret ending in Mortal Kombat: Deception, he explains his fight with the Elder Gods in the Void "beyond the One Realm", which can be inferred to mean that everything (including the Heavens) were also merged into the One Realm, except Onaga and the Void and at the time, the Elder Gods. Whether the One Realm can be accessed to in the Nexus is also unknown. It is possible that the realms' original appearance can also be distorted or changed completely during such a fusion. Ironically, Onaga used the Kamidogu to do the exact thing the Elder Gods feared in the end - the realms becoming whole and the One Being coming back. The only known case of the creation of the One Realm was in Onaga's secret ending in Deception. However, this is non-canon to the Mortal Kombat plot. After Shujinko destroyed the six Kamidogu in his quest, he made it impossible for such a thing to happen.