If Naruto was born before the Second Shinobi War, the story would be drastically different. For one, the political landscape of the ninja world at that time was very different. There were different power struggles and alliances. Naruto might have grown up in a more chaotic and war - torn environment. His presence could have potentially changed the outcome of some of the battles during the Second Shinobi War. Maybe he could have influenced some of the key players in a way that would lead to a different future for the ninja villages.
In a fanfiction where Naruto is born during the Second Shinobi War, he could potentially be a major asset to the Leaf Village much earlier. Since he's the jinchuriki of the Nine - Tails, his power could be harnessed for the war effort. However, this also means he'd be in more danger from enemy villages who would want to either capture or kill him. His relationship with the villagers might be different too. Instead of being shunned for the Nine - Tails inside him, they might see him as a necessary evil for the village's survival.
If Naruto was born during the Second Shinobi War in fanfiction, he might have more battle - hardened powers. He could potentially have a better control over the Nine - Tails' chakra from a younger age due to the need to fight in the war. His Rasengan could be developed in a more combat - oriented way, perhaps with added elements of destruction to take on stronger enemies.
The relationship with the village elders would be complex. They might have seen him as both a great hope and a potential liability. His relationship with the other Jinchuriki could also be different. If he was known earlier as a Jinchuriki, he might have been in contact with others, like Gaara, earlier. And his relationship with Sasuke would have an added layer. Maybe Sasuke's family would have seen Naruto in a different light, knowing he was born before the war and had some sort of special significance.
He could meet the young Hiruzen Sarutobi. Naruto might learn a lot from him about the history and politics of the shinobi world at that time. They could also exchange jutsu knowledge to some extent.
Potential allies? Well, Jiraiya for sure. Jiraiya was always interested in unique and powerful ninja. If Naruto was born earlier, Jiraiya would likely be drawn to him. And maybe some of the members of the Uzumaki clan who were still alive at that time. They could have guided Naruto in using his clan's unique abilities. Enemies? The Akatsuki could have emerged as enemies much earlier. Their goals were often in conflict with the stability of the ninja world, and Naruto, with his powerful potential, would be a target for them.
Well, in a fanfiction where Naruto is born before the Third Shinobi War, it could mean that the prophecy about him might have been known earlier. This could have led to different training methods for him. Maybe the Sannin would have been more involved in his upbringing. Jiraiya could have started training him much earlier, and Tsunade might have been more focused on his physical well - being. Orochimaru, on the other hand, might have seen him as an earlier opportunity for power and tried to manipulate him much sooner. All these changes would have a huge impact on the overall Naruto storyline.
Well, perhaps Naruto could find himself in the middle of a crucial battle during the Second Shinobi War. He could befriend some of the young shinobi who later become important figures. He might help them out in a difficult situation, like rescuing a group of shinobi from an ambush. This would change the course of the war in small ways and also form strong bonds with those from the past.
It could be an original character. For example, a young ninja from a small, unassuming clan that has been overlooked in the grand scheme of the war. But as the war progresses, they show extraordinary skills and courage, becoming a key figure in the battles.
Well, the plot could revolve around a shinobi who has a special ability that is both a curse and a gift. During the Second Shinobi War, this shinobi is hunted by different factions because they believe his ability can be used to tip the scales of the war. However, the shinobi doesn't want to be a part of the war and is constantly on the run. In the end, he might be forced to use his ability to save a large number of people, including those from the villages that were hunting him, and in doing so, he changes the perception of his ability.