One possibility is that Naruto, with his godlike abilities, could completely rewrite the history of the ninja world. He could go back to the time of the Sage of Six Paths and learn from him directly. This would give Naruto an even greater understanding of chakra and ninjutsu. He could then introduce new forms of training and cooperation among the ninja villages, perhaps even preventing future wars. He could also ensure that the jinchuriki are treated better in the past, changing their fates for the better.
One possible plot could be that godlike Izuku uses his newfound powers to go back and prevent certain tragedies in the past. For example, he might stop the initial attack that led to so much chaos in his world. He could also use his knowledge of the future to help his friends earlier, like giving Midoriya tips on how to control his quirk better from the start.
He could change the course of major events. For example, he might prevent the rise of a powerful villain. This would have a huge impact on the entire galaxy. Maybe he could save some characters who died in the original timeline.
In this fanfiction, Sora might change key events. Maybe he could prevent some of the tragedies that occurred in the original story. For example, he could save a character who was lost before.
She might change important events in the wizarding world. For example, she could prevent certain dark magic incidents or save characters who died in the original timeline.
Well, he might meet his ancestors. It could be really interesting to see how they interact and what kind of influence he has on their lives. Maybe he'll change some small events that end up having a big impact on his present time.
In this kind of fanfiction, Jotaro might change some crucial events. For example, he could prevent some of his friends from getting hurt or even stop the main villain from starting their evil plans at an earlier stage. This would completely change the original story's timeline and create a whole new set of adventures and challenges for Jotaro and the other characters.
Well, he might prevent some of the villains from ever becoming powerful. For example, he could stop Frieza from getting all those power - ups.
Well, she might meet historical figures. For example, she could encounter Cleopatra and have an interesting conversation about ancient Egyptian politics and culture.
In the 'Petunia Goes Back in Time' fanfiction, she might try to change things that happened in the past. Maybe she wants to fix a mistake or prevent a bad event from occurring.
One possibility is that Draco could try to change his family's fate. In the original story, his family was on the wrong side of the wizarding war. By going back in time, he might attempt to steer them towards a more positive path, perhaps by preventing them from getting involved with Voldemort in the first place.