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.
One idea could be a story where the character with the Rinnegan avatar has to navigate a world where the rules of chakra and bending are combined. For example, they might use the Rinnegan's powers to control different elements in a way similar to how avatars control them in the Avatar world.
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.
Maybe the Avatar, in his journey to master all the elements, travels to the Naruto world. He could learn some ninja techniques and incorporate them into his fighting style. The Avatar could also teach the ninja about the power of bending, which could lead to some really unique team - up strategies among the characters.
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.
Another plot idea is to have a character who is not Naruto, perhaps a new OC (original character), inherit the knowledge of the Reaper Death Seal in an unexpected way. This character could then face the moral dilemma of using such a powerful and dangerous jutsu.
Perhaps the nine - tailed fox in Naruto and the Avatar state could have some sort of connection. In the fanfiction, the two powers could interact in unexpected ways. For example, when Naruto enters his nine - tailed fox mode, Aang's Avatar state could be affected, or vice versa. They might have to learn to control these interactions to save both their worlds from a dark force that wants to use this power connection for evil.
Well, a great plot for 'naruto crimson avatar fanfiction' could be centered around a tournament. Naruto and his friends enter a tournament where they have to use their new Crimson Avatar powers. But there's a catch - the tournament is being secretly manipulated by an old enemy who wants to steal these powers for themselves. The characters must not only compete but also figure out the enemy's plot and stop them.
Perhaps in the 'immortal naruto avatar fanfiction', Naruto's immortality is a curse at first. He has to figure out how to control it while also dealing with the political unrest in the Avatar world. He might form an alliance with the Avatar to bring peace. This would involve a lot of character development as Naruto struggles with his condition and tries to do good in a foreign land.
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.
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.