Avatar: Fire Emperor

Water, earth, fire, and air-those who can control one of these elements are known as benders. As a result, four nations arose in the world: the Water Tribes, the Earth Kingdom, the Fire Nation, and the Air Nomads. Among them, only the Avatar can master all four elements at once. The Avatar serves as a bridge between the four nations, maintaining the balance of the world. However, a hundred years ago, the Avatar suddenly disappeared. Seizing this opportunity, the Fire Nation launched a war of aggression against the other three nations-a conflict that has lasted for nearly a century. At this time, Kahn transmigrated into this world and became a young firebender… — Description from novelcodex.org