Kanna, referred to by her grandchildren as "Gran Gran", was Katara and Sokka's caring paternal grandmother. She was a nonbender and the oldest resident of the Southern Water Tribe. Although Kanna initially distrusted Aang, once he was revealed to be the Avatar, she regained hope, something, she remarked, that she had not felt for a long time.
Kanna was born in 19 AG to a family in the Northern Water Tribe, and when she reached the marrying age of sixteen, it was arranged that she would marry Pakku, a young waterbender. Following the tribe's engagement tradition, Pakku carved a betrothal necklace for her. Though he loved her deeply and thought their marriage would be successful, she harbored a strong distaste for the Northern Water Tribe's chauvinistic social standards for women, which Pakku vehemently supported. As a result, Kanna felt despaired and searched for a way out of the marriage. Sometime before their wedding, Kanna fled her homeland and traveled to the Southern Water Tribe. Although she left without notice, she did take the necklace with her.
Kanna, while still a young woman, befriended Hama, one of the Southern Water Tribe's most skilled waterbenders, and the two experienced the Fire Nation's first raids on their tribe together. Although Hama and her fellow waterbenders fought intensively, they eventually succumbed to the invasions, and when she was taken onto the Fire Nation vessel, Kanna was the last face Hama saw before she was locked away.
Years passed, and the Hundred Year War continued to stress the Southern Water Tribe's warriors and resources, making Kanna somewhat bitter and cynical. Her son later became the tribal chief and married a woman named Kya, who eventually gave birth to Sokka and Katara, Kanna's only grandchildren. Kanna later passed on her engagement necklace to Kya, and Kya passed it down to Katara. Kanna never told her grandchildren the history or significance of the necklace, or of her past in the Northern Water Tribe.
The year prior to the return of Sozin's Comet, Kanna's grandchildren discovered an iceberg concealing an airbender in suspended animation named Aang. They freed him and brought him back to their village, and in agreement with her grandson, Kanna did not trust the stranger and came to view him as a threat when he accidentally triggered a Fire Nation flare used by PrinceZuko as a signal for attack. She was among the people who asked for Aang's departure from the tribe and persuaded her granddaughter to stay with them despite her longing to travel with the young monk to a place where she could learn waterbending.
Nevertheless, the village was attacked by the Fire Nation and Kanna was directly threatened by Zuko. Aang quickly came to the rescue, revealing himself as the Avatar, and surrendered to protect the villagers. Following this, Kanna allowed Katara and Sokka to leave in order to save Aang and assist him in his goal of mastering all four elements, as she recognized that this was their ultimate destiny.
After the Siege of the North, Kanna reunited with Master Pakku, who had ventured to her home with some other people from the Northern Tribe in order to provide assistance in rebuilding the Southern Water Tribe. Pakku later carved Kanna a new betrothal necklace and the two were eventually married.
Kanna seemed to have sported the same hairstyle, hair loopies, her whole life.
Kanna looked very much like Katara when she was younger, as Yugoda suggested.
Originally, Katara's name was to be Kya. However, when Nickelodeon vetoed the choice of name, the creators renamed her Kanna, which stuck for a few weeks before they decided to name her Katara. Kya became the name of Katara's mother, while Kanna became Gran Gran's name.
Kanna strongly resembled the wise elder women found in many of the works of Hayao Miyazaki – most notably, the Wise Woman who starts Prince Ashitaka on his quest in Princess Mononoke. The series' creators have professed their fandom of Hayao Miyazaki in many interviews.
Katara and Kanna helped deliver many infants in the Southern Water Tribe.