Air
Airbending · BaguazhangCircles and evasion: never meet force head on. Four temples, and after the comet, one airbender left.
Franchise · Primary · 2005 – 2008
Avatar: The Last Airbender
The best-written cartoon ever made, and it is not particularly close. Four bending arts, three books, sixty-one episodes, and a war ended without the hero breaking his own rule.
Water
Waterbending · Tai chiPush and pull, and the strength of the full moon. The only art that also heals.
Earth
Earthbending · Hung GarRooted, direct, immovable. Neutral jing: listen, wait, and strike at exactly the right moment.
Fire
Firebending · Northern ShaolinBreath first, aggression second, and after the dragons, a nation that forgot the difference.
FireSozin · Roku
AirAang
WaterKorra · Kuruk
EarthKyoshi
Avatar
The cycle
One Avatar per generation, reborn into the next nation in a fixed order: fire, air, water, earth, and round again. Roku was Fire, Aang is Air, Korra is Water, and Kyoshi was Earth four hundred years before either of them.
Each Avatar starts with the element of their own nation and learns the other three in cycle order, which is why Aang has to go water, earth, fire, in that sequence, with a war on and a comet coming.
The Avatar State opens every past life at once. The catch is permanent: die in it and the cycle ends there, for good.