So Sokka's the avatar, but with a twist ;) Sokka was discovered to be the avatar and taken to the royal palace where he grew up with Zuko and Azula. He was taught that what the fire nation was doing was actually good, that he was the key to helping the fire nation to achieve their goals, but when Sokka hears that all he can see is the suffering his village had because of them, how can that be good? He's been planning to escape for years, but the opportunity never presented itself until one day Zuko is challenged to a Agni Kai, using it as a distraction and sure Zuko could beat some dumb general he escapes and steals a ship to find himself a way to win the war and he'll do it without some dumb bending, even if he needs to learn some dumb bending tricks along the way.