A popular plotline is Kyuubi's backstory being explored in more depth in the fanfiction. There might be details about its past, its original relationship with the Sage of Six Paths, and how it came to be sealed inside Naruto. This can add a whole new layer of understanding to the Naruto universe. Also, some fanfictions have the Kyuubi acting as a sort of protector of Naruto in a more conscious way, rather than just being a source of power. It might help Naruto in battles by giving him strategic advice or by using its own chakra in a more intelligent way.
One common plotline is the Kyuubi teaching Naruto new and powerful jutsu. Since the Kyuubi has a vast amount of chakra and knowledge, it could share unique techniques with Naruto that are not part of the regular ninja training. Another plotline could be the Kyuubi's influence on Naruto's relationships. For example, some fanfictions explore how Naruto's connection with the Kyuubi affects how his friends and villagers perceive him. It can also lead to some interesting character development as Naruto has to learn to control the Kyuubi's power without being consumed by it.
A theme that is often explored is the mystery surrounding the Kyuubi. Fanfiction authors like to dig deeper into the origins and secrets of the Kyuubi. This might involve things like the Kyuubi's past relationships with other powerful beings or the true nature of its power that has not been fully revealed in the original series.
One common plotline is Naruto's discovery of his true parentage. He might initially be shocked or in denial but then gradually come to accept it. Another is his training to master the combined powers of the Kyuubi and Juubi. This often involves seeking out ancient scrolls or mentors who have some knowledge about these powerful entities.
One common plotline could be the conflict that arises between fem Kyuubi's possessiveness and Naruto's own desires for freedom and friendship. Naruto might want to explore and interact with others, but the fem Kyuubi tries to hold him back.
A possible fanfiction could be set in an alternate universe where Naruto, Kyuubi, and Tsunami are all part of a prophecy. They have to journey together to find a sacred relic that can either save or destroy the ninja world. Along the way, Naruto has to constantly balance the power of the Kyuubi within him, and Tsunami uses her survival skills and knowledge of the world to help them overcome various obstacles.
Another theme is the Kyuubi's backstory. Fanfictions may delve into the origin of the Kyuubi, its past relationships with other powerful beings in the 'Naruto' universe. This can add a whole new layer of depth to the overall story.
In Naruto fanfiction, Kyuubi can help Naruto by providing him with extra power. For example, it can enhance Naruto's physical abilities like strength and speed during battles. This allows Naruto to face stronger opponents more easily.
Well, a possible plotline is that Naruto has to deal with the fact that he has the power of the Kyuubi in a more innate way. Maybe he discovers that he can access certain abilities that are unique to being the son of Kyuubi, like a deeper connection to the chakra of the nine - tailed beast. There could also be a plotline where the Akatsuki target him not just for the Kyuubi's power but because of his special connection to it as its son. And his own village might have to decide whether to protect him or sacrifice him for the greater good.
One interesting plotline could be Naruto gaining new and powerful abilities after the merge. For example, he might be able to access a new form of chakra that combines his own with the Kyuubi's. This could make him nearly unbeatable in battles against strong foes.
One possible plotline could be Naruto gradually losing control over his own actions as the Kyuubi's influence grows stronger. For example, he might start to act more aggressively towards his friends without realizing it.
One interesting plotline could be Naruto gaining new and unique powers from the merge. For example, he might be able to access a special form of chakra that combines his own with the Kyuubi's, allowing him to perform super - strong jutsu. Another could be how his relationships with his friends and allies change. Maybe some are initially afraid of his new power, but he has to prove that he's still the same Naruto at heart.