Sokka, Katara, and Yue all end up on Appa searching for Aang. Sokka doesn't know how safe it is for Yue to leave the Northern Water Tribe, but she figures the princess is safest with her and her sister.
Sokka's surprised to find herself saying something almost kind about Zuko and his inability to give up.
They find Aang and Zuko. Katara knocks Zuko out and Aang makes them bring him along so Zuko doesn't freeze to death. Sokka wishes Aang wouldn't be so kind.
When everything turns red, Yue starts to not feel good. When she tells them the story of how the Moon Spirit saved her life, Sokka can't help but fear that something very bad is about to happen.
Zhao kills the moon spirit, Zuko gets away, and everything goes wrong.
"It gave me life, maybe I can give it back." Yue says to the old man Sokka has seen with Zuko before.
"No!" Sokka protests. "You don't have to do that." She says reaching to stop Yue.
"It's my duty, Sokka."
"I won't let you." Sokka held tightly to Yue's arm. "Your father told me to protect you."
"I have to do this." Yue's hand slipped out of Sokka's when the princess placed her hand on the koi fish. The koi began to glow as Yue closed her eyes for the last time.
Sokka caught her. "No!" She cried out. "She's gone," Tears filled Sokka's eyes. "She's gone."
The entire lake began to light up and the energy floated up in the air to form an image of Yue. "Good-bye, Sokka." Yue leaned her forehead against Sokka's. "I'll always be with you." The princess kissed the top of Sokka's forehead before disappearing. Sokka peered into the koi pond and saw that a single thick streak of white was now in her hair. Sokka saw the moon now reflected in the pond and looked up towards it. The color in the sky came back.
Later, after the Fire Nation is finally gone, Sokka stands on a ledge looking at the moon with Arnook.
"I'm so sorry I let this happen to you daughter Chief Arnook."
The chief put his hand on Sokka's shoulder. "The spirits gave me a vision when Yue was born. I saw a beautiful, brave, young woman become the Moon Spirit." The chief sighs. "I knew this day would come."
"You must be so proud." Sokka said, her eyes on the moon.
"So proud… and sad."