One idea could be to explore the backstories of the avatars in the brotherhood. Maybe they all come from different worlds or cultures and how they came together to form the brotherhood. Another could be a story about a new avatar joining the brotherhood and facing challenges to be accepted.
A great idea for a brotherhood avatar fanfic would be to focus on the training and development of the avatars. Show how they learn to master their abilities, and how their relationships within the brotherhood change as they grow stronger. You could also include some elements of mystery, like a hidden power or prophecy that only the avatars can fulfill.
Well, you could write a fanfic where the avatars in the brotherhood have to face a powerful enemy that threatens their existence. They then have to use their unique powers and the bond of brotherhood to defeat it. Or perhaps a story where there is a rift within the brotherhood due to a misunderstanding, and how they overcome it.
One idea could be exploring the backstory of a minor character from the Avatar world in the sequel fanfic. For example, a Na'vi who was on the fringes of the main events but has their own interesting journey. Another could be a story about the first human - Na'vi hybrid, dealing with identity issues and being a bridge between the two cultures. Or perhaps a fanfic that focuses on the restoration of a part of Pandora that was damaged during the events of the movie, showing how the Na'vi and any sympathetic humans work together to heal the land.
One idea could be a crossover where Naruto characters learn bending techniques from Avatar characters. For example, Naruto might try to master water bending, which could be a really cool concept as he already has control over his chakra, and adapting it to bending could create some unique fight scenes.
A different plot could be about a power struggle within the Brotherhood. There could be a group of members who think the current leadership is too soft on dealing with the enemies. This could lead to internal conflicts, with some members trying to overthrow the current leaders while still having to face the external threats to their kind.
One idea could be to have the Voltron pilots end up in the Avatar world. They could learn bending techniques and use their Voltron skills in combination with them. For example, Keith's swordsmanship might blend well with waterbending moves in a fight.
Perhaps Ben, while exploring a new planet in his travels, stumbles upon a world that has a very Avatar - like culture and power system. He has to learn to use their ways in combination with his alien forms to survive. For example, using Heatblast's heat powers in a more refined way similar to firebending.
Another aspect might be the development of new relationships. Characters that didn't interact much in the original could form deep bonds in the fanfic. This could lead to new storylines and character growth. For instance, a Fire Nation character and an Earth Kingdom character becoming friends and working together to overcome a common threat.
One idea could be exploring the relationship between the new characters introduced in Avatar 2 in more depth. For example, a fanfic could focus on the friendship or rivalry between two young Na'vi from different clans. Another plot could revolve around a human character who becomes stranded on Pandora and has to learn to survive with the help of the Na'vi. They could discover new areas of Pandora that were not shown in the movie, filled with unique flora and fauna. A third idea might be a fanfic that delves into the backstory of one of the main Avatar 2 characters, perhaps their family history or how they came to be in their current position.
One idea could be exploring the early life of a new Na'vi character. Maybe they grew up in a different part of Pandora and had unique experiences with the local flora and fauna that are not shown in the movie. For example, they could have a special bond with a rare creature that helps them in a time of crisis later in the story.
One idea could be Naruto having an encounter with a death - like entity that grants him new and dark powers. He might struggle with the morality of using these powers while still trying to protect his village.
A plot could revolve around a group of avatar students from different tribes who are brought together for a special project. They initially clash due to their different cultural backgrounds and ways of using their avatar abilities. But as they face challenges together, they learn to work as a team and understand each other better. For example, a fire nation student might be impatient with the slow and methodical approach of a water tribe student when it comes to solving a problem related to their powers.