Well, Naruto might gain some new powers or knowledge from having Tobi sealed. Maybe he could access Tobi's memories and use that information to prevent future threats.
The story in this fanfiction might progress as Naruto discovers new things about Tobi's past while he is sealed. This could lead to revelations about the overall plot of the Naruto world. As Naruto delves deeper into Tobi's secrets, he may also face opposition from those who fear the power he now holds with Tobi sealed within him. His relationships with his friends and allies could be tested as they try to decide whether to trust Naruto or not with this new power.
Well, he might start being more mysterious like Tobi. He could start using more deception in his actions, for example, hiding his true intentions from his friends just as Tobi often did. Maybe he'll also start using some of Tobi's speech patterns or ways of interacting with others in a more indirect and puzzling way.
He could be portrayed through his appearance. For instance, one personality might have different - colored eyes or a distinct style of dressing. His behavior would also change. When in one personality, he could be very talkative and energetic, and when in the other, he could be silent and brooding.
Definitely Kakashi. Since he has a connection to both Naruto and Tobi (Obito), his presence can add a lot of depth. He can be the one who tries to bridge the gap between Naruto and Tobi, or he could be a source of conflict as he has his own history with Tobi.
One interesting Naruto and Tobi fanfiction could be where Tobi reveals his true identity to Naruto earlier in the story. This would completely change the course of events and their relationship. Naruto might try to reason with Tobi, believing there is still good in him.
Perhaps it could be due to some ancient and forgotten jutsu that was cast on him unknowingly. There are many powerful and mysterious jutsus in the Naruto universe. Maybe during one of his adventures or even in his early childhood, a jutsu was activated that messed with his mind and created this second personality. It could also be related to his Uzumaki heritage. The Uzumaki clan had many secrets, and maybe this second personality is a manifestation of some latent genetic trait that was triggered by certain events in Naruto's life.
Maybe he's on a secret mission. He could be trying to infiltrate an enemy group that Tobi was associated with. By acting like Tobi, he hopes to gain their trust and gather information.
If Naruto had Gaara's personality, the story would be very different. Naruto is usually outgoing and boisterous, while Gaara is more reserved and initially cold. With Gaara's personality, Naruto might not be as quick to make friends. He'd be more guarded and less likely to trust others easily. This could change his relationships with characters like Sasuke and Sakura. His interactions with the villagers would also be different. Instead of trying to gain their approval through big shows of strength and determination, he might keep more to himself, which could slow down his journey to becoming Hokage.
Fanfiction should be a creative and positive space. 'Naruto tobi pedo fanfic' involves inappropriate and immoral themes. In the Naruto fandom, there are so many positive aspects like the story of friendship, growth, and ninja adventures that can be explored in fanfic, rather than this kind of disturbing content.