— Onaga, in his secret ending for Mortal Kombat: Deception.
The One Realm is a name given to the outcome of merging all the realms into one existence. The only known means of creating the One Realm is with the power of the One Kamidogu. 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, Vaeternus, 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 battle 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 be distorted or changed completely during such a fusion. The One Realm can be fused with other dimensions and/or beings, as was the case in the secret ending of Onaga. 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. Towards the end of the opening scene of Deception, Shujinko narrates "Now Onaga has what he needs to shape the realms as he sees fit" referring to his plans of creating a realm in his image. 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 ever happen.
- The One Realm was mentioned in Li Mei's Mortal Kombat: Deception ending when the young Outworlder turned on her former allies and gave her emperor the time he needed to finish merging all the 6 Kamidogu into one and thus he succeeded. Li Mei watched in delight as the Elder Gods fled in fear of the newly powerful Onaga before he transformed her into his queen to be with him forever as they would soon together rule the One Realm for all eternity.