One idea could be a crossover where Ben 10's Omnitrix malfunctions near Avatar Aang's world. Ben and Aang team up to face a new threat that is causing chaos in both their realms. Maybe some of Ben's alien forms have unexpected interactions with the bending abilities in the Avatar world.
In a fanfiction, the Avatar State of Aang could be used in a more creative way. For example, Aang accidentally enters the Avatar State during a cultural festival. His friends are initially worried, but then they realize that in this state, Aang can communicate with the spirits present at the festival in a unique way. He learns secrets about the spirits and their connection to the human world, which he then uses to strengthen the bond between the two realms when he's out of the Avatar State.
One common theme is power control. Aang often has to learn how to handle the immense power of the Avatar State without losing himself. For example, in many fanfictions, he struggles with the sudden influx of energy and the potential for destruction it holds.
One common theme is friendship. Since Aang is a central character, the stories often explore how he forms a deep friendship with the female avatar. They support each other, learn from one another, and grow together.
One great Aang fanfic could be one where he has to face an unexpected new threat in the Spirit World. It might explore his growth as the Avatar even further, showing his unique connection to the spirits and how he uses airbending in creative ways to overcome challenges.
Yes, there are quite a few interesting 'Avatar Aang and Katara' fanfictions out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Some fanfictions explore their relationship further after the events of the show, delving into their daily lives and how they grow together.
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.
Avatar Aang was a very important figure in the Avatar universe. One appropriate story could be about Jinora learning from Aang's teachings. For example, Jinora might study the way Aang brought balance to the world and use that knowledge to help solve problems in her own time. She could be inspired by Aang's courage in facing the Fire Nation and apply that to standing up against new threats in her community.
Another aspect is the relationships in the fanfic. Aang has important relationships with Katara, Sokka, Toph, and others. If a fanfic can develop these relationships in new and interesting ways, it's great. For instance, a story where Aang and Katara have a misunderstanding that they need to work through, which could test their relationship and show their individual growth as characters.
One popular plotline is Aang and Zuko teaming up to face a new threat to the Four Nations. Maybe a long - lost ancient evil that requires both the Avatar's bending skills and Zuko's strategic mind. Another is a story where they go on a journey to understand each other's pasts better. This could involve visiting places that were significant in their respective childhoods.