Xaa is a realm mentioned in the Mortal Kombat cartoon series Mortal Kombat: Defenders of the Realm.
This realm consists entirely of a jungle-like wilderness with huge spikey rocks, and an empty Asian-styled, temple-like castle at the center of the realm. Not much is known about this strange other dimension, other than it is one of certain realms including Outworld where Raiden has no dominion and is apparently powerless there, as well.
When Princess Kitana's old friend Rain, arrived in Earthrealm. He and his band of rebels dedicated to her father's memory, bring news the that Shao Kahn and his forces are prepared to lay claim to Xaa and steal a scimitar hidden in a temple within that realm. And with that scimitar that has have been said to defeat many warriors with one strike, Kahn would crush all any enemy and rebellion that stood in his way. Kitana agreed to go with him but Liu Kang among his friends who barely trusts him, was more concerned for Kitana. Raiden appeared and agreed to open the portal to Xaa.
But when they arrive, they were attacked by a siege of scarlet demonic creatures appeared out of a portal but they beaten them and got them on the run. That moment Rain unleashes a smoke pillar and took Kitana with him to the portal. Raiden arrived in Xaa and tells the Earth warriors that they are needed back in Earthrealm, revealing that the scimitar, Shao Kahn's invasion of Xaa and Rain's rebel group were all a lie. Liu Kang and Kurtis Stryker chose to stay behind to rescue Kitana.
When inside the castle in Xaa, both of them were attacked by Motaro and his fellow Centaurs that are guarding Rain and Princess Kitana on behalf of Shao Kahn. Motaro was beaten and the Centaurs were distracted by Stryker while Liu Kang is free to go rescue her. Liu Kang open the secret passageway through a fountain within the castle's antechamber using his chi. He then entered a cavernous chamber where Kitana was to be sacrificed to a green creature with five insectoid heads and four arms with three claw-like fingers. Liu Kang defeated the beast and saved Kitana. They regroup with Stryker and tried to escape Xaa, but they were all stopped by the traitor Rain. Kitana decided to beat Rain by herself. Rain uses a stone spiked club from the armory of his "castle" to attack Kitana, but she easily bested him and won. But the pillars destroyed by Rain during the fight, could no longer support the structure of the castle, leaving the entire building beginning to crumble. Rain escaped and Raiden appeared to rescue Kitana, Liu Kang and Kurtis Stryker and take them back to Earthrealm. The castle in Xaa was completely destroyed.
Source
Defenders of the Realm - Skin Deep