Well, in this type of fanfiction, perhaps Naruto in the Kyuubi's place would gain a deeper understanding of the Kyuubi's power and its origin. He could also communicate with the other tailed beasts in a different way. As for the Kyuubi in Naruto's place, it might have to face Naruto's emotional struggles, like his longing for acceptance from the village. This could lead to some unexpected character development for both Naruto and the Kyuubi.
If Naruto and the Kyuubi switch places, his friends might be initially very confused. They are used to Naruto's normal behavior. If the Kyuubi is in Naruto's body, it might be more aggressive or act in ways that seem out of character. His friends would have to figure out what's going on. But if Naruto is in the Kyuubi's place, his friends might start to worry about him more, not knowing what he's experiencing inside the seal.
Naruto, if in Sasuke's shoes, would inherit Sasuke's goal of revenge against Itachi and later, those who were involved in the Uchiha massacre. His life would be centered around getting strong enough to exact justice. Sasuke, in Naruto's place, would focus on the well - being of the village. He'd want to show that he was more than just a powerful ninja, but also a reliable protector. He'd work towards building relationships with the villagers and would be more open to the idea of becoming Hokage, which was Naruto's original aspiration.
Naruto's friends in the Hidden Leaf would be really confused if Harry showed up. They'd wonder why he doesn't know basic ninja stuff. Harry's friends at Hogwarts would be equally baffled by Naruto. Hermione might try to study Naruto like he's a new magical creature. Ron would probably be a bit more hesitant around Naruto at first.
Yes, in some fanfictions, Naruto is often depicted as the Kyuubi or having a very close connection to it. This can lead to really interesting and unique storylines that deviate from the original plot.
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.
In many Naruto fanfictions, Naruto might have developed some new and unique abilities that the Kyuubi has no defense against. This could make the Kyuubi, which is used to being a dominant and feared force, feel vulnerable. For example, if Naruto has the power to nullify the Kyuubi's chakra or to manipulate it in a way that goes against the Kyuubi's will, it would be a cause for fear.
Maybe it's because Naruto has some sort of special connection or resemblance to the Kyuubi that Kushina notices. For example, Naruto might display some of the Kyuubi's power characteristics in an obvious way that makes Kushina jump to that conclusion.
At first, Naruto might see the Kyuubi as just a source of power. But as he starts to protect it, he realizes it's more of a partner. Their relationship evolves from a simple user - power source dynamic to a deep - seated friendship. He begins to understand the Kyuubi's emotions and past, which further cements their bond.
Sasuke is often a popular character in these fanfictions. His relationship with Naruto can be further explored in the context of the Kyuubi's fatherly influence. Maybe Sasuke is initially skeptical of this new - found bond between Naruto and the Kyuubi but later comes to accept it. Sakura is also a common character. She might notice the changes in Naruto due to the Kyuubi's fatherly presence and be either supportive or a bit jealous. Kakashi could also be there. He might be observing Naruto's growth under the Kyuubi's guidance and offer his own wisdom as Naruto's former teacher.