Tui

"spirit"

- The legends say the moon was the first Waterbender. Our ancestors saw how it pushed and pulled the tides and learned how to do it themselves.

Tui, the Moon, was one of two spirits which resided in the Spirit Oasis at the North Pole, in the Northern Water Tribe's capital city. She and La circle each other in an eternal dance.

History
Thousands of years ago, Tui and her counterpart La decided to manifest themselves in the physical world to better benefit mankind, taking up residence in an alcove of the Northern Water Tribe's capital city. Thus, the Spirit Oasis in the city became its most treasured landmark. Tui's physical form resembles a white koi fish, with a large black spot on its head.

When she was a baby, Princess Yue was taken by her father, Chief Arnook and his wife to the Spirit Oasis. She was seriously ill, very weak, and on the brink of death. He dipped her in the waters at the Spirit Oasis, her black hair turned white and she started crying. Although Tui did grant healing to Yue, Chief Arnook had a dream that one day Yue would have to take Tui's place as Moon Spirit.

Many years later, the Fire Nation launched a siege on the capital city of the North. Steadily, the Fire Nation navy advanced upon the city, eventually destroying its protective locks and dams and advancing onto its icy surface. Admiral Zhao, the leader of the attack, advanced with his personal guard to the back of the royal palace to kill the Moon Spirit, as he had thought to do so ever since he had discovered the existence of the Spirits in the mortal world from Wan Shi Tong's library. In a scoop, Zhao caught Tui in a bag of water, causing the spiritual equivalent of a lunar eclipse, destroying the power of the Waterbenders worldwide. However, Iroh stepped in and threatened Zhao, telling him whatever he did to the moon spirit, he shall do to him, but ten times worse. To the horror of Katara, Aang, and General Iroh, Zhao murdered Tui anyway, under the guise of releasing her, destroying the power of the moon altogether. Iroh, in anger, lashed out at Zhao, incapacitating his guards. Zhao, however, slipped away, only to be attacked by Zuko. Meanwhile, Aang fused with La and destroyed the Fire Nation invasion force.

Iroh then realized that Yue had some of Tui's life energy, since it had bonded with her to save her life when she was born. Yue then made the ultimate choice: to sacrifice her life in order to resurrect Tui, against Sokka's objections, since he was in charge of protecting her. Once this happened, not only did the moon return to its full power, but Yue's physical body disappeared from Sokka's arms and reformed as Yue's spirit form, making Yue the new Moon Spirit. In this form, she kisses Sokka one last time and disappears.

By having her life force energy re-bond with Tui, Yue not only was reincarnated as Tui's successor, but she gained the ability to Waterbend, a trait she didn't carry in life. Her abilities were seen to some extent in The Awakening, when Yue generates a massive wave for Aang to ride on, towards the island where Roku's Temple once stood.

Trivia

 * "Tui" (推, tuī) means "push" in Chinese. According to Princess Yue, the ancient waterbenders saw the tides push and pull giving a hint to the moon spirit's existence in the tribe.
 * In The Last Airbender film, Zhao associated the Moon Spirit with Yang (white, male) and Pull (拉, Lā), a different convention than the animated series. As such, Yue refered the Moon Spirit as male, "He gave me life when I was a child."