The Last Airbenders: Book One

Four years prior to the birth of Aang, Roku died, but was brought back, causing the Avatar Spirit to split. This fragment of the Avatar Spirit was imbued into a young airbender named Ann-Ji. This young girl chose the "Avatar toys" when she was a small child. However, because Avatar Roku was still alive, she was not acknowledged as the next Avatar. Four years after her birth, Roku passed without any possibility of revival, resulting in the birth of her half-brother, Aang. When placed in front of the toys that were to be chosen, Aang chose the same ones Ann-Gee and all other past Avatars had. They acknowledged him as the Avatar as Roku was no longer alive. Twelve years later, Ann-Ji was visiting her brother in the Southern Air Temple. When she was visiting, also happened to be when Aang was deciding to run away. Ann-Ji was going to try to persuade him to return, so she was hidden away in Appa's saddle. Then they encountered the storm that threw them into the ocean. To protect themselves, both Aang and Ann-Ji ended up freezing themselves in ice for one-hundred years, only to be found again by two siblings from the Southern Water Tribe.