Avatar: The Last Airbender Season 3 Episode 16 : The Southern Raiders
The Avatar and his friends are forced on the run again after Azula finds them in the Western Air Temple. Zuko confronts Katara about her distrust of him and tries to gain her friendship. He decides to help Katara find the Fire Nation soldier responsible for killing her mother, despite Aang's warnings that violence is never the answer. Together they find the soldier known as Yan Rha (now retired), where Katara discovers that her mother died protecting her, the last waterbender in the tribe. Despite Katara's uncontrollable anger, she is unable to take revenge on him. Katara and Zuko leave, while Yan Rha falls on his knees, lamenting his wrongful past actions against her. After returning, Katara finally forgives Zuko.