In such a fanfiction scenario, it can have a huge impact on the plot. Future Naruto has more experience and knowledge. He can train past Naruto in advanced techniques, like better control of the Nine - Tails' chakra. This could potentially change the course of battles in the past. For example, in the fight against Pain, past Naruto might be able to use new skills taught by his future self to win more easily. It also might change Naruto's relationships. If he becomes stronger faster, his friends might view him differently, and enemies might be more cautious.
There are quite a few things. For one, he could teach past Naruto about the deeper secrets of the Uzumaki clan. Since Future Naruto has explored more about his heritage. He could also give tips on handling the Kyuubi's chakra more smoothly. Maybe some new jutsu combinations that he discovered over the years. And not to forget, how to better read an opponent's moves during a fight, which is a skill he would have refined over time.
One possibility is that future Naruto could give past Naruto some advice on how to handle his relationships better. For example, with Sasuke. He might tell him to be more understanding and patient. Also, future Naruto could show past Naruto some of his new jutsu and inspire him to train harder to reach that level.
In a fanfiction like this, Orochimaru could train Naruto in the ways of stealth and assassination, skills that Orochimaru is quite proficient in. Naruto would initially be hesitant but realizes that these skills can be used for good. For example, to infiltrate enemy bases and gather intelligence to prevent wars. This would change Naruto's fighting style and make him more versatile in the shinobi world.
The meeting could also have an impact on Naruto's relationship with his village. If future Naruto shares with past Naruto how important it is to have the trust and support of the village in the long run, past Naruto might focus more on building bridges within Konoha. This could lead to a more united village earlier in the story and change the way they face external threats.
The older characters such as Kakashi would be cautious. They would recognize Naruto but also be worried about the implications of someone from the future being in the present. They would want to know if his presence could change the future in a negative way. For example, they might fear that his actions could lead to the earlier awakening of a powerful enemy. As for the villains, they might see future Naruto as a threat and try to eliminate him as soon as possible. Orochimaru, for instance, would be very interested in Naruto's future powers and might try to capture him to study. And the new generation of ninja in the past would look up to future Naruto, seeing him as a symbol of what they could become.
There could be a focus on Naruto learning new forms of the Rasengan. Hokage Naruto, with his vast experience, could teach Naruto different ways to infuse the Rasengan with other elements more easily. Maybe Naruto would learn how to quickly switch between a Fire - Rasengan and a Wind - Rasengan during combat.
One way is through time - travel jutsu. A character could accidentally or intentionally use a jutsu that sends them to the future or past. For example, Naruto might find a hidden scroll with a time - travel jutsu and end up in the future where he sees how his friends and the village have changed. This could lead to interesting storylines where he tries to fix things or learn from the future.
In this fanfiction, it could also be about Naruto going back in time to learn from Kakashi. Since Kakashi was a great ninja in the past, Naruto might want to gain some skills or wisdom that he didn't have the chance to learn before. They could form a unique bond during this time, different from their relationship in Naruto's original timeline. Kakashi could be initially suspicious of this strange Naruto from the future but gradually come to trust and mentor him.
One possible plot could be that Naruto from the past somehow gets a glimpse of the future of Konoha. He sees new threats emerging and starts training in ways that can counter those threats in the future. He might also try to influence the present actions of his friends and allies based on what he saw in the future.