In The Legend of Korra, which takes place 70 years after the events of Avatar: The Last Airbender, we know that Katara lived a long life and eventually became a mentor for the next Avatar.
Katara and Aang shared their first kiss in The Last Airbender season 2, episode 2, "The Cave of the Two Lovers." However, they didn't officially become an item until the first last episode of the series, "Sozin's Comet Part 4: Avatar Aang," when they kissed again in the wake of her brother, Sokka, who is already dead by the time The Legend of Korra begins. However, her old friends Zuko and Toph are still alive in the sequel series.
Katara lived through an interesting time in the history of her world, as the lines between the Four Nations blurred and a new country emerged: the United Republic of Nations. The defeat of Ozai was followed by an industrial revolution and great leaps forward in technology. By the time The Legend of Korra begins, Katara is 85 years old and living in a world with radio and moving pictures. Here's everything that happened to Katara after Avatar: The Last Airbender's ending.
Katara Returns Home To The Southern Water Tribe
The Avatar: The Last Airbender comics pick up immediately after the end of the series and detail the early days of Aang, Zuko, and other leaders building a new world out of the ashes of the Hundred Year War. Katara goes on various new relationship with Aang (they call each other "sweetie," a habit that gives Sokka the "oogies"). However, Katara's biggest story in the comics comes when she returns home to the Southern Water Tribe in the trilogy "North and South," only to discover that the village she grew up in has become a massive sprawling city. The Northern Water Tribe, having discovered vast reserves of oil underneath their sister tribe's lands in the south, plan to build a refinery and turn the Southern Water Tribe into the source of precious fuel for all Four Nations as the industrial age emerges.
Katara is upset by how much her home has changed since she's been gone, and even more upset when she learns that her and Sokka's father, Hakoda, has a new girlfriend: a Northern Water Tribe architect called Malina. Now head chieftain of the Southern Water Tribe, Hakoda is helping Malina and her brother with the so-called Southern Reconstruction Project. However, insurgent forces within the Southern Water Tribe believe (correctly) that the Northern Water Tribe is using the city construction and the building of the refinery to turn the south into effectively a colony of the north. A tribesman called Gilak attempts to kill Hakoda and take his place as chieftain, but Katara is fortunately able to use her healing powers to save her father's life after he is stabbed.
By the end of the comic, Katara comes to accept that she and Sokka will never have their simple village life back again, and even accepts her father's new relationship with Malina. Though Gilak's attempted usurpation is stopped, the tensions that arise in "North and South" don't go away. In The Legend of Korra season 2, a civil war breaks out between the Northern and Southern Water Tribes, eventually culminating in the Southern Water Tribe declaring its independence.
Katara's Marriage To Aang, Children & Grandchildren
Katara and Aang have three children. The eldest, Bumi, was named after Aang's childhood friend and the King of Omashu. Living up to his namesake, Bumi has a wacky personality and enjoys telling wild stories that may or may not be true. Born a nonbender, he served as a naval commander within the United Forces. Katara and Aang's middle child, Kya, is named after Katara and Sokka's late mother. She is a skilled waterbender just like Katara, and is particularly skilled in the art of healing. Finally, Katara and Aang's youngest son is called Tenzin - an homage in the show to Aang's mentor, Monk Gyatso (the current Dalai Lama's name is Tenzin Gyatso). Tenzin is the only airbender of the three children (that is, until Bumi gains airbending abilities in The Legend of Korra season 3), and was therefore under the greatest pressure from Aang to rebuild the Air Nomad civilization and culture.
Through Tenzin, Katara has four grandchildren: Jinora, Ikki, Meelo, and Rohan. Unfortunately she doesn't get to see them often, as they live on Air Temple Island in Republic City, while Katara still lives with the Southern Water Tribe. When Tenzin brings his children to see Katara in The Legend of Korra's pilot, Meelo struggles when she picks him up and say, "Unhand me, strange woman!", and it's generally implied that the children only see their grandmother every few years. However, the older children do refer to her as "gran-gran," just like Katara and Sokka once called their own grandmother.
Katara Teaches Waterbending To The Next Avatar
The Avatar reincarnates through each of the Four Nations in a cycle, so after Aang's death the next Avatar was born into the Water Tribes. Perhaps by fate, Korra was born into the same Southern Water Tribe that Katara came from, and so after Aang's death she was able to watch over her late husband in his new life as a feisty young waterbender. Growing up in a sheltered life within the Southern Water Tribe, Korra is trained in the art of bending by different masters who are brought to the city. Katara, who was established as being an unusually skilled waterbender in Avatar: The Last Airbender (Master Pakku said that she learned faster than any other student he has taught), becomes considered to be the greatest master of waterbending in the world.
Naturally, Katara trains Korra in both waterbending and healing. However, she never teaches her the dark art of bloodbending, and in fact has bloodbending made illegal in the United Republic of Nations. Avatar: The Last Airbender fans will recall that Katara learned bloodbending in the season 3 episode, "The Puppetmaster," but was so horrified by it that she vowed never to use it again. She broke that promise once, when she and Zuko went looking for the man who killed her mother, but aside from that slip-up it seems like Katara continued to eschew bloodbending for the rest of her life.
Katara comes to Korra's aid again in The Legend of Korra season 3, after the Avatar has suffered great physical and psychological trauma following a battle in the spirit world that leaves her without the use of her legs. Over the next two years, Katara aids in Korra's rehabilitation and helps her to walk again. She reminds Korra that Aang also suffered greatly after learning his entire culture had been wiped out, but he channelled his suffering into helping people. And so, through Katara, Aang's wisdom is ed on to Korra as well.
