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The group recovers from the fall of Ba Sing Se, and travel to the planned invasion site. On the day of the solar eclipse, Aang's group and a smaller band of warriors launch a smaller invasion, which ultimately fails. Zuko confronts his father and defects from the Fire Nation. After a series of events, he manages to gain the trust of the protagonists and becomes Aang's firebending teacher. Aang and Zuko unlock the true secrets of firebending from the ancient "Sun Warriors", Sokka and Zuko later travel to a Fire Nation prison called the Boiling Rock to rescue Sokka's father and Suki, a warrior from Kyoshi Island.

On the day of Sozin's Comet, Fire Lord Ozai harnesses the comet's incredible power and energy to start a genocidal campaign to destroy the rest of the world. Aang and his friends split up to face the self-proclaimed Phoenix King Ozai, Azula (about to be crowned as the new Fire Lord), and the Fire Nation air fleet accompanying Ozai. Aang confronts and defeats Ozai. Zuko and Katara defeat Azula before her coronation. Sokka, Toph, and Suki destroy the air fleet. Zuko becomes the new Fire Lord and promises to help the world rebuild from one hundred years of war and suffering.