Been having this idea bounce around in my head for a while now and I figured I had a basic enough synopsis that if someone else with better literature skills was given all of this they could come up with a fun series.
Main Character: An earthbender avatar whos family got killed in a caravan by Buzzwasps when he was a newborn, sandbenders found the wreckage and him and took him in, the sandbender tribe earning money as a cargo hauling company moving cargo through the desert, has one of those water walking lizards that Azula and her possee used during the chase as his mount and some sort of small desert critter as his animal companion. When he was 5 he started painting the dunes seen outside a window in his room every day because he was fascinated by how they changed a little every day. Surprisingly chill due to viewing the world as a constant flux and will have an easier time with sand rather than actual earth.
First Ally: A former Red Lotus member, the two of them crossing paths is what incites the main plot and joins the main character after having their eyes opened to the fact that human nature is neither Order nor Chaos, but Change, feel free to add whatever you feel for this one
Basic Plot: Two years after the end of the LoK cartoon, Korra had a nightmare about her future incarnations either cursing her out or dieing due to inexperience, so for the rest of her life she spent her time training in pretty much everything, every form of combat, both armed and unarmed, bending or nonbending, she trained in as many as she could, at the same time she found a way to locate the spirits of the past avatars in the spirit world and re-establish their connection with the light spirit Raava, most of them were annoyed but understanding that some parts of that were just out of her control, and by the time she passed away she had reconnected with over 200 due to her determination to make things right. Meanwhile the Dark Spirit Vaatu, after his vessel Unalaq was killed, bided his time while latched onto the spirit, forcing his reincarnated form to practice in all 4 bending styles, and while Raava's connections and sheer numbers gave the Light Avatar an impossible to replicate control over the elements, Vaatu was able to make up for it by forcing the Dark Avatar into a twisted, ferocious and powerful style that sacrificed any skill for raw damage and output.
Meanwhile the MC discovers what happened to his real parents 16 years into his life, the stress and pain of learning what he's lost triggers the Avatar State, causing him to see Korra's spirit talking to him and explaining everything I just talked about with her, urging him to try and continue the same for the sake of the world. Obviously having so much pressure put on him at once freaks him out and he refuses, but entering the Avatar State alerted the Red Lotus, now a Yiga-like faction that hides in the shadows and worships Vaatu, who sends one of their newest recruits in hopes of assisting the Dark Avatar.