So basically, I got an idea of a firebending Avatar after Korra and the unknown earthbender Avatar (another idea) living in a post-apocalyptic world of the Avatar world as we know it, in the aftermath of an all-out nuclear war. Leaving the world barren and arid, the war also exterminated much of the human population, flora and fauna. However, the cycle of the Avatar continues on, like the four seasons, and the next in line to carry on the duty of the Avatar was born as the young firebender Arakan (Japanese for Hero).
The idea is still in a very early stage of development, so I'd love to hear your thoughs and ideas. However, I've managed to scrap together a basic setting.
The world consists of a large desert-like dry landscape due to the aftermath of a nuclear war, and the polluted gas is slowly killing all life it comes over. Much of the oceans have dried up, and the few humans left live isolated from one another in seperated communities. The poles remain unchanged, with the portals still intact, leaving the whole world inhabited by hostile spirits, who lurk in the woods and the dark (much like the Spirit Wilds). In a village on top of trees, hidden from aggressive spirits and the pollution in the air, young Arakan discovers in an age of 13 that he indeed possesses the qualities of the Avatar and that he is destined to bring balance to the world by making humans and spirits co-exist, and saving the planet from the poisonous gas. After getting successfully located by the remnants of the Order of the White Lotus, Arakan decides to travel the world to master the elements and gather knowledge in order to create an ideal world for humans and spirits. On this journey, he encounters trustworthy companions and greedy foes. I thought of an ending to the series where the world eventually collapses and he has to bring his people to live in the Spirit World, where they encounter new opportunities and dilemmas.
Arakan: A young firebending Avatar who travels the world to gather knowledge and strenght. He learned of his fate early so he had to sacrifice much of his childhood where he would spend time climbing trees and challenging travelers to Agni Kai duels. He is kind, brave, stubborn, mischievous and rebellious. Although he is childish and reckless of nature, he would sacrifice anything to save those he cares about.
Taiyo: A golden phoenix that Arakan found and befriended as a baby, in a cave. They've been lifelong friends since then, and their bond is unbreakable. His loyalty for his friend is undying and he also serves as a useful means of transportation (flying). He is mostly seen taking it easy, napping and so on, but when danger is approaching he is quick to defend his friend. He is the last of his kind and has a rare ability to firebend.
Udita: Not much is known about this mysterious and concealed ninja-warrior. She has a mass arsenal of weaponry, and mainly uses her katana and shuriken. She is completely wrapped up with clothing and armor. She used to live in the desert, scavenging and raiding travelers, until she attempted the same against Arakan, who quickly defeated her with a blast of fire. Although she rarely speaks, she recognizes Arakan's strenght and resolve and thus earns her respect. They became stuck with eachother, and although she doesn't really have a goal in life, she decides to stick with him because it brings her joy somehow.
Yomi: The loyal black cat of Udita, usually sitting on her shoulder and observing her surroundings. Like her master, she is very quiet but not to be underestimated, as her quick reflexes and sharp claws can prove fatal in combat.
Central City: A city-state lead by Emperor Cyphus, a ruthless dictator and his personal advisor, Doctor Kendrell. Their goal is seemingly to create a haven for humans to live in this highly technologically advanced society, at the cost of spirit energy and deforestation. After many failed warnings from the Avatar to stop waging war on the spirits, the city has constructed an elite team of energybenders to hunt down the Avatar and wipe him out of their way to finally achieve their ambitions.