In the events after Kuvira and her army invaded Republic City, Asami and Korra leave for the Spirit World for a much needed vacation together. However, what they find on the other side is not the Spirit World…
Instead what they see is a what seems to be an endless expanse of white with a single large looming door and what appeared to be a person the sorts of which Korra and Asami had never seen. Though it had a rather creepy smile the person had no discernible eyes or nose it didn't even have hair. Its skin, or what they assumed was skin, was completely white edged with a odd looking black aura.
"Hello" it said as it looked up from nothing.
"Um... this isn't the Spirit World is it?" asked Korra after gawking a few more seconds.
"No, this is the Source of all Truth, this is all, and this is nothing." it replied cryptically.
"Well this worse than trying to commune with all the past Avatars, when I still could of course"
"Yeah, nothing like cryptic messages and riddles." Asami chipped in "So um what do we call you?" she continued.
"Me? You can call me Truth." it said grinning wider.
"Okay so... how do we get to the Spirit World or back to Republic City, Truth?"
At this Truth stopped grinning and with a sorry look he opened the door behind him and said "You cannot go back yet, you are both being called for in another world which is currently in peril." At this the two glanced at each other shocked by what Truth said.
"What do you mean we can't go back yet?!" they exclaimed in unison.
"Right now there is a country called Amestris in a world that has far more differences than similarities to your own. For one no has ever heard of bending of the four elements in that world instead they use equivalent exchange through a process called alchemy. However you will still be able to bend there. I will integrate you into their society give you enough knowledge about their world, what it is you are doing, and about someone who will help given you can pique his interest in you..." said Truth
"Alright fine, but as soon as we're done there send us to the Spirit World so we can finally have our vacation." said Korra clearly aggravated by Truth.
"Yeah we'll help so long as we are needed." Asami agreed.
Truth's grinning returned "Good step through the door and you will wake up in the Military Hotel. You Korra will be given the position of State Alchemist nicknamed the 'Energy Alchemist' and Asami you are going to be a military engineer working on a flying machine for aerial combat and reconnaissance." with that they walked toward the door and disappeared.