A possible plot is that Naruto in the past meets his parents when they were young. This would be a very emotional and complex situation. He would have to hide his relationship to them while also trying to protect them. And he could use this opportunity to understand more about his family and the history of the village from a different perspective.
One interesting plot could be Naruto using his future knowledge to prevent some tragic events in the past. For example, he might stop the death of certain characters or change the course of a big battle.
In this type of fanfiction, a possible plot is that Naruto is sent to a dimension where time moves differently. He might age at a much faster rate, and he has to quickly master the ways of this dimension to find a way to reverse the time effect on him. Another cool plot could be that he lands in a dimension that is a mirror image of his own, but with opposite personalities for everyone. So he has to deal with a Sasuke who is overly friendly and a Kakashi who is always serious, which makes for a really strange and challenging adventure.
In this type of fanfiction, a great plot can be Naruto going back and influencing the Third Hokage's decisions. For example, he could convince the Hokage to be more open - minded about new techniques and alliances. He might also focus on improving the living conditions in the village at an earlier stage. By doing so, he could potentially change the future of the entire Hidden Leaf Village and the shinobi world in general.
Perhaps in the fanfiction, Naruto's past catches up when he discovers that he has a long - lost relative who has a unique power. This relative might be on a different path, either good or bad, and Naruto has to figure out how to deal with this newfound family connection. It could involve a lot of emotional turmoil as he tries to understand his place in this new family dynamic.
One interesting plot could be Naruto using his future knowledge to prevent the Uchiha massacre. He might try to change Itachi's situation and find a way to resolve the conflict between the Uchiha clan and the village without all that bloodshed.
One interesting plot could be Percy's struggle to survive in Tartarus alone. He might have to face the various monsters there without his usual allies. Another plot could involve him finding a way to escape Tartarus using his wits and the powers he has. Maybe he discovers some secrets about Tartarus that no one else knows.
Well, in some fanfictions of this kind, Harry might face a cruel caretaker in the orphanage. But instead of being beaten down, he uses his wits and hidden magic to stand up for himself and the other kids. He could also start to learn magic on his own, using his natural instincts, which would be a really cool plot.
One interesting plot could be Naruto using his future knowledge to prevent the death of some important characters like Jiraiya. He might be able to warn Jiraiya about Pain's true identity in advance and change the outcome. Another plot could be Naruto influencing the relationship between Sasuke and the village earlier, preventing Sasuke from leaving in the first place. He could also use his experience to train more effectively from a young age and become even stronger faster.
One interesting plot could be Naruto using his future knowledge to prevent some of the tragedies that happened in the original story. For example, he might be able to stop the Uchiha massacre. Another plot could be him training his younger self, leading to a much stronger Naruto earlier on. And perhaps he could also change the relationship between the different ninja villages, promoting more peace and cooperation from an earlier stage.
A plot where the past and future ninja teams have to compete in a tournament. Each team has their own set of skills and strategies based on their time periods. The past teams might rely more on brute force and basic jutsu, while the future teams have more advanced and unique jutsu. It would be a great opportunity to see the evolution of ninja techniques and how the different generations interact.
One interesting plot could be that Harry Potter is sent to an alternate universe where magic is used in a completely different way. For example, instead of using wands, they use hand gestures. Another plot might be that in the alternate universe, Voldemort won in the original world, and Harry has to find a way to reverse that in this new universe. Maybe in this alternate world, the Hogwarts houses have different characteristics and he has to adapt to that new social structure as well.