One idea could be a crossover where Naruto, with the power of the Kyuubi, somehow ends up in the world of Legend of Korra. He could team up with Korra to face a new threat that combines the dark jutsu from Naruto's world and the bending abilities in Korra's world.
Perhaps a fanfiction could explore what would happen if the Kyuubi's chakra was infused into the Avatar state in the Legend of Korra universe. This could give Korra an unprecedented boost in power and a new set of abilities to master. She might have to learn to control the wild and powerful nature of the Kyuubi's chakra while still maintaining her connection to the four elements.
Another plot could be set in a post - Naruto and post - Legend of Korra world. A descendant of Naruto who still has a connection to the Kyuubi's power discovers an ancient relic from the time of Korra. This relic holds the key to a great power or a great danger, and they must journey across both worlds, learning about the history of both Naruto and Korra's eras, to decide what to do with it.
One possible plot idea could be a crossover where characters from Naruto and Legend of Korra have to team up to face the Juubi. Maybe the Avatar from Legend of Korra discovers a new power that is linked to the chakra of the Juubi in the Naruto world.
One idea could be a story where Naruto and Korra meet in a dimension where the worlds of their respective shows collide. They could team up to fight a new, powerful enemy that threatens both their universes. Another idea is a time - travel story where Korra goes back in time to the Naruto era and has to adapt to the different ninja world while also sharing her bending knowledge.
One idea could be a time - travel plot where Korra is sent back in time to the era of Naruto. She has to adapt to the different world and also help Naruto in some way, like against a new threat that she has knowledge of from her own time. Another could be a crossover adventure where they both end up in a strange new dimension and have to rely on each other's skills to find their way back home.
One idea could be that the reincarnated character has memories of their past life. They could use this knowledge to predict events in the Avatar world. For example, they might know about an upcoming threat and start preparing for it much earlier than anyone else. This could lead to some interesting interactions with Korra and the other characters as they try to convince them of the danger.
For Legend of Korra fanfiction, you could write about an alternate universe where the Avatar cycle is broken. Korra has to figure out how to fix it while dealing with the chaos that ensues. You might also consider a story where Korra forms an unexpected alliance with a group of non - benders who have developed their own form of combat to rival bending. Additionally, a fanfic that delves into the relationship between Korra and Asami in more depth, showing their daily lives and how they contribute to the rebuilding of Republic City together, would be really engaging.
One idea could be exploring Korra's early training days in more detail. Maybe she has a secret adventure during that time that wasn't shown in the original series. Another could be a fanfiction where Korra has to team up with an unexpected ally from the Spirit World to save Republic City from a new threat. A third idea is to write about what would happen if Korra lost her bending abilities for a while and had to learn to fight and defend without them.
One idea could be exploring the bond between Naruto and the Kyuubi in a new way. For example, they could have a shared dream where they are in a strange, alternate world and have to work together to find a way back. Another plot could involve Naruto using the Kyuubi's power to save a village from a new, powerful enemy that no one else can defeat. And a third could be about the Kyuubi revealing a long - lost secret about Naruto's family that changes his perspective on his own powers.
Maybe there's a time - traveling plot where Korra gets sent back in time to Naruto's era. She has to adapt to the different ways there, and Naruto helps her. Along the way, they are intrigued by each other's powers and personalities. They go on adventures together, facing challenges side by side, which leads to a romantic connection.
One idea could be a crossover with another popular fantasy world like 'Harry Potter'. Korra could end up at Hogwarts and have to deal with magic in a completely new way. Maybe she'd use her bending to enhance or counter some spells.
One idea could be that Ichigo, through some sort of interdimensional rift, ends up in the Avatar world of Legend of Korra. He could initially be seen as a threat due to his otherworldly powers. But as the story progresses, he teams up with Korra to fight a common enemy that is trying to take over both their worlds. His Soul Reaper powers could be used in unique ways, like using his Getsuga Tenshou to blast away dark spirits that are plaguing the Avatar world.