One idea could be that their kids discover a new bending technique that combines air and water bending in a unique way. For example, they create a sort of ice - air blast that can freeze and shatter objects simultaneously. Another plot could involve the kids going on a journey to learn about their parents' past adventures and in the process, they face challenges that test their own bending skills and teamwork. They might encounter an ancient spirit that only responds to a combination of air and water bending, and they have to figure out how to work together to communicate with it.
Maybe a plot where Aang and Katara's family gets involved in a diplomatic mission to the Fire Nation. Their children are exposed to a different culture and way of life. Along the way, there are some misunderstandings and cultural clashes, but in the end, they manage to strengthen the relations between the nations. And during this time, the family also discovers a hidden secret about the Fire Nation's past that could change everything.
One common plot idea is Aang and Katara facing challenges in their relationship due to their different cultural backgrounds. For example, Aang being an Air Nomad and Katara a Water Tribe member.
One plot idea could be a story where Aang and Katara have to face a new threat together that specifically targets their relationship. Maybe a dark spirit tries to create misunderstandings between them by making Aang see false visions of Katara being unfaithful and Katara seeing Aang as being too controlling. They then have to work through these false impressions and reaffirm their love for each other.
One idea could be that they dance at a festival in the Water Tribe. Aang is initially clumsy but Katara patiently teaches him the traditional Water Tribe dance steps. As they dance, they share memories and their bond deepens.
One interesting Katara and Aang fanfiction could be about their adventures after the end of the original series. Maybe they travel to new lands and discover new bending techniques together. Another could be a story that focuses on their relationship development during a time when the Fire Nation is trying to make a comeback. There are also fanfictions that might explore an alternate universe where Katara and Aang meet in different circumstances, like if Katara was from the Fire Nation and Aang was from the Water Tribe.
Another fanfiction could explore the challenges they face during Katara's pregnancy. Since Aang is the Avatar, he has many responsibilities. There could be a conflict where he has to leave for an important mission, but he doesn't want to leave Katara alone. Katara, being strong - willed, tells him to go and fulfill his duties. In his absence, she discovers new water - bending techniques related to pregnancy and childbirth, which she plans to teach other women in their community later.
There could be a fanfiction where Katara discovers she's pregnant during a journey. They then have to cut their adventure short and return to a more stable place. Along the way, Aang uses his airbending to keep Katara comfortable during the pregnancy, like creating gentle breezes to cool her when she's feeling hot. This would show their love and care for each other during this special time.
One interesting story could be that Aang and Katara meet in a different time period, like in a modern world. They have to adapt to new technologies while still maintaining their connection. Aang might be fascinated by things like cars and airplanes, and Katara could be intrigued by modern medicine.
The kids would likely be very kind - hearted like Aang. Aang was always about peace and helping others, so his kids would probably inherit that trait. They might also have Katara's strong will. Katara was never one to back down when she believed in something, and the kids would have that determination too. For example, if there was an injustice in their village, they would be the first to stand up and try to make it right, using both their air and water bending powers.
Well, perhaps Katara is kidnapped by a bounty hunter who has been hired by someone who has a vendetta against the Avatar's team. The kidnapper could be taking her to a far - off and desolate location. Then, Aang and the others have to track her down through various difficult terrains. Or, it could be that she's kidnapped by a group of dark benders who want to study her waterbending to find a way to corrupt it. They might keep her in an underground lair filled with all sorts of dark magic - like contraptions.