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.
In a naruto x avatar fanfiction, there could be a scenario where the Akatsuki from Naruto's world teams up with some of the villains from the Avatar world. This would force Naruto and the Avatar (whichever one it may be) to put aside their differences and form an alliance with other characters from both worlds to stop this powerful and evil coalition.
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.
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.
A really interesting plot would be if the Nine - Tailed Fox in Naruto had some sort of connection to an ancient and powerful spirit in the Avatar world. The Avatar and Naruto would have to figure out this connection and use it to either control or understand the power of the Nine - Tailed Fox better. This would involve a lot of exploration of both worlds' mythologies and powers, and also some great character interactions as Naruto and the Avatar learn from each other.
Another plot could be that Naruto is mistaken for an Avatar in the Avatar world. As he tries to clear up the misunderstanding, he gets involved in local politics and relationships. The female characters see his honesty and kindness, and gradually, a harem - like situation develops around him.
One idea could be that Naruto somehow gets transported to the Avatar world and his unique ninja skills draw the attention of multiple female characters. They might be intrigued by his determination and power, leading to a harem - like situation where they all vie for his attention.
One popular plot idea is a crossover where Naruto characters end up in the Avatar world. For example, Naruto could learn bending techniques and use his ninja skills in combination with them. Another idea is a story where the Avatar has to learn from Naruto's way of never giving up. Also, a plot could involve the Akatsuki trying to take over the Avatar world for its resources.
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.
Perhaps the Akatsuki from Naruto somehow get involved in the Avatar world's politics. Their goals of collecting tailed beasts could be translated into a search for some powerful Avatar - related artifacts. This would stir up a lot of chaos in the Avatar world and force the Avatar and his friends to team up with some Naruto characters to stop them.