Fury Road AU

In the conclusion of the Hundred Year War, the Fire Nation was successful in using the return of Sozin's Comet to virtually wipe out the Earth Kingdom. The continent was left nearly entirely barren, and the massive loss of plant life and vegetation had disastrous, unforeseen consequences on the global environment. Due to the atmospheric imbalance caused by the sudden lack of forestation, exacerbated by pollution from developing technologies, the polar ice caps melted rapidly, causing sea levels to rise. The Fire Nation archipelago was partially subsumed, and the Fire Lord collapsed shortly thereafter.

Roughly eighty years later, those who continue to survive in the former Earth Kingdom usually do so in isolated groups, which tend to settle around scare resources, such as water. Asami Sato grew up in the remnants of Yu Dao, which by that point was run by an especially vicious and tyrannical warlord. Water and food were scarce and tightly controlled, and her mother died when she was young. Due to her father's value as an engineer, however, she lived in comparative comfort and learned her father's skills, though an accident involving the machinery she helped her father maintain resulted in her losing her right leg below the knee when she was twelve. As she grew older, her father worried her beauty would attract the warlord's attention, and he decided they should try to leave. Asami convinced him to take a number of refugees with them. Though they managed to flee the compound, they were initially pursued, and Hiroshi was killed during the escape. Asami continued on, planning to take the refugees to the only known remaining green place on the continent (the Swamp), but encountered a group led by the new Avatar. The group took in the refugees, and Asami agreed to join the Avatar, who planned to end the warlords' reign and restore the world.

(So, basically, Imperator Asami.)