The Firebending Masters

While teaching Aang the basics of firebending Zuko discovers that his own firebending has grown severely weaker. After some thought, he realizes that this is because he is no longer filled with anger and hatred, which used to fuel his fire. In order to discover the true, original source of firebending, him and Aang travel to the ruins of the Sun Warrior Tribe, which consisted of the first humans to learn firebending. Once there, they quickly discover they are not alone.