This is just a summery of a fan fic I'm thinking of continuing to writing. It's a crossover between Avatar and Resistance. I already wrote one chapter, but for now I'll just post a prologue.
Set many years after The Legend of Korra. The Four Nations are at war, but not against each other but an alien race known as the Chimera. They attacked the Four Nations out of nowhere. Despite the surprise attack the Four Nations stood their ground and were able to withstand the intial attack. At first the Four Nations thought they could easily take on the Chimera, but they soon found outhow wrong they were. Soon more Chimera ships come to Earth and they brought the Chimera Virus. The Chimera Virus was a virus they converted people into Chimera. 2 weeks later the Air Nomades were whiped out. 5 months later the Water Tripes were lost.
It's been 5 years since the war started. The Fire Nation is barly standing and most of the Earth Kingdom is under Chimera control. With no cure for the Chimera virus and the Chimera gaining more gorund, the people begin to lose hope and the Avatar is nowhere to be seen.