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.
One great Aang fanfic is 'Aang's New Adventure'. It takes place right after the end of the series. In this fanfic, Aang has to deal with some leftover Fire Nation rebels who don't want to accept the new peace. It's really exciting as it shows Aang using his bending skills in new and creative ways to bring about peace once again.
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.
In the 'Avatar: The Last Airbender' series, there are no real love stories between Azula and Aang. Azula is a complex antagonist, while Aang is the heroic Avatar. Their relationship is mainly one of opposition, with Azula constantly trying to thwart Aang's mission to save the 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.
A really interesting fanfic I read had Aang and Katara having a disagreement over how to deal with a new threat. Aang believes in a more peaceful approach, while Katara thinks they need to be more forceful. This creates tension between them, but as they work through it, they realize that they need to combine both their ideas. It's a story that really delves into their characters and how they complement each other.
Common themes often include friendship and how it can transform into something more. Also, the idea of breaking traditional boundaries. In these fanfics, Aang may be facing challenges that come with being in a relationship that goes against the norm in his world. And there's often a focus on the emotional journey, like how he deals with his new - found feelings and the reactions of others.