Avatar Survivor Chronicles
I have an ATLA theory, as people believe if aang never ran off after believing gyatso woidlnt be his master, that he woidl have died in the massacre, but i dont beleive so as the avatar state woudl activate to keep him alive (as we see in canon and its nit until after the lightning from azula thta aang struggles with it) so likely he woudl survive it while being traumatised and still hopefull (confuswd mainly and greaving) as he is lured into the airnomad refugee camps by the fire nation (as we see mentioned by zhao in canon) he would survive it and spent the next years battlimg and ambushing fire nation troops while being hunted (he wpild onlt have 2-3 of the elemwnts (not fire and maybe not water (he is a prodigy in it but he woudl have earth due to bumi)).
As he dies the next avatar is a water avatar likely arpund pakku or hama generation (could even be a swamp bender who never gets involved into the war inthe forst place); lets go with the hama route, her story is very similar to canon except during the southern raids its hama entering the avatar state that causes the ship to be held in ice, thoufh she passes our aoon after as she is sti capturwd but ita in xaptivity under the full moon and avatar state that she unlocks bloodbending, as she escales and frees a few other water benders as she spends thw rest of her life in hiding taking out some fire natiom patrols and troops in the night and she leaves till old age close to the time line of the canon story.
As she dies the next avatar is a earth avatar from the earth kingdom, Toph Beifong a blind rich girl babied by her parents for her percoeved frailty, though she secretly enters the avatar state as a child whoch causes a coty wide tremor and sink holes as she is stuck underground she learns earth bending fr thw badgermoles as after the incident (percieved as anatural distater but also allerting the fire nation) she is babied even more by her parents which incentives her secrelty rebellious personal in thw blind bandit in the underground arena (and her avatar journey woudl just go on from there) (this also fits in the canon systematic hunting of the nations during the 100 year war (air due to going after aang, water for his successor amd earth for the one after thata (though in canon it was stalled due to aang being on ice)). I call this "Avatar Survivor Chronicles"