Avatar: The Last Airbender Season 2

Avatar: The Legend of Aang Season 2; Avatar: The Last Airbender (Book 2: Earth)

In this season, the protagonist Aang and his friends Katara and Sokka are on a quest to find an Earthbending teacher which finishes when they recruit Toph Beifong. After finding important information concerning the war with the Fire Nation, Appa ends up kidnapped. Their journey leads to Ba Sing Se, the capital of the Earth Kingdom, where they uncover great internal government corruption.