The older brother in the fanfiction might be a character with a tragic past. For example, he could have been experimented on by Orochimaru and gained some strange powers as a result. And he returns to the village later to protect Naruto from the threats that are coming towards him.
In the fanfiction, the older brother could change Naruto's view of his family and his place in the world. Naruto would have a connection to his past that he didn't know before. This could lead him to explore more about the Uzumaki clan and discover hidden powers or knowledge. And it could also affect his relationships with Sasuke and Sakura. For instance, his brother could help him understand Sasuke's pain better, leading to a different dynamic between them.
Well, in this fanfiction idea, Naruto being Sona's older brother could bring a whole new dynamic. Maybe Naruto's protective nature would extend to Sona. He could teach her some of his ninja skills and values like never giving up. It could also create interesting interactions with the other characters in their respective universes. For example, how would the devils in Sona's world react to Naruto's presence? And how would Naruto handle the political aspects of Sona's world which are quite different from his own ninja village politics.
There could be. Fanfiction writers like to explore different 'what - if' scenarios. Since Naruto and Kushina have a strong connection in the original series, some writers might be intrigued by the idea of reversing their relationship in a fictional context. But it goes against the established lore of the main Naruto storyline.
In some fanfictions, it's possible for Naruto to be depicted as Anko's older brother. Fanfiction often takes creative liberties with established characters and their relationships.
If Naruto was the older brother of Kushina, it would rewrite a lot of the backstory. For one, Naruto might be the one to introduce Kushina to Minato. He could see Minato's potential and think he would be a good match for his sister. Also, Naruto's skills and abilities could have a different origin. Maybe he learned some things from Kushina or their family that were unique. This would change his fight scenes and how he approaches challenges in the fanfiction. He might also have a different relationship with the Uzumaki clan as a whole, having more of a family - based influence within it.
One idea could be that Naruto, with his strong sense of justice and loyalty, helps Rias in the supernatural politics of her world. He might use his ninja skills to protect her and her peerage from other devils or threats. For example, when facing a powerful rival devil clan, Naruto's shadow clone jutsu could create a diversion while Rias plans a strategic attack.
In a fanfiction where Naruto is Madara's older brother, it could completely change the Naruto universe's dynamics. For example, Naruto's ideals of peace and friendship might have influenced Madara at a young age, preventing him from going down the dark path he did in the original story. Naruto could have taught Madara about the power of bonds, which was something Madara seemed to have lost sight of later in his life. This would lead to a different series of events, perhaps even averting the many wars that took place in the Naruto world.
Yes, there are likely some fanfictions with this concept. Fanfiction writers often explore unique relationships and alternate storylines. They might create a scenario where Naruto is Sasuke's older brother to develop different character dynamics, explore new plotlines, and add their own creative twists to the Naruto universe.
Perhaps in this fanfiction, Naruto has to keep his identity a secret from Minato. He could be from an alternate future where things went wrong, and he's there to make sure Minato becomes Hokage and prevents certain disasters. So he has to subtly guide Minato without revealing who he really is.