Perhaps Naruto's brother could be a long - lost relative from a far - flung part of the ninja world. He could have been separated from Naruto when they were young due to a war or some political intrigue in the ninja clans.
In this kind of fanfiction, Naruto might have an emotional reunion with his brother. Maybe they would exchange stories about their pasts, and his brother could share some family secrets that Naruto never knew.
His brother could be an unknown Uzumaki. Since Naruto is from the Uzumaki clan, it would make sense for his brother to be from the same clan. Maybe he was hidden away for some reason, like to protect him from the same threats that Naruto faced as a child.
In the 'naruto meets his brother fanfic', it's possible that the brother has a different view of the ninja world compared to Naruto. This could lead to some interesting debates between them. The brother might be more cynical or have a darker past that Naruto has to come to terms with. There could also be a rivalry at first, but as they get to know each other better, they form a strong bond. Maybe the brother has some special abilities that Naruto has never seen before, and Naruto is eager to master those abilities as well.
It could be an unknown brother that was kept secret all this time. Maybe he was hidden away by some enemy of the village and trained to be a powerful adversary for Naruto.
One possible reason could be jealousy. Maybe his brother has some special abilities or gets more attention that Naruto feels he should have. For example, if his brother is really good at a certain jutsu and is always praised for it while Naruto struggles, that could lead to resentment.
If Naruto meets his parents in fanfiction, one possibility is that they would be able to train him in ways that no one else could. Minato could teach Naruto advanced ninjutsu techniques, especially those related to the Flying Thunder God Technique. Kushina could help Naruto better control the Nine - Tails' chakra, as she was once its jinchuriki too. This meeting could also give Naruto a sense of belonging that he has always craved.
In the world of Naruto fanfiction, the theme of Naruto killing his brother does exist. It might be a way for some authors to create a more edgy and different take on the Naruto story. They might rewrite the story's lore and Naruto's personality to make such a scenario possible. For example, they could create a backstory where there is some great conflict between Naruto and his brother that leads to this tragic outcome. This can also be a way to explore different power dynamics and the cost of power in the Naruto world.