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.
There are several potential characters. Aizawa could be one. Godlike Izuku could show up in the past and Aizawa might be suspicious of his powers at first but then come to realize his good intentions. Gran Torino is also a possibility. Izuku could learn different things from him in the past. And then there are the other pro - heroes. They might see Izuku as a strange new force but also recognize his potential to do good. His interactions with them could change the course of hero history in this fanfiction.
Well, it could be that Izuku goes back in time and tries to change the way he became a hero. In the original story, he had a tough time at first. With Momo by his side this time, things could be different. Momo might be able to provide resources or support that Izuku didn't have before. And as Izuku tries to change his own hero journey, he might also end up changing the entire hero society in ways he didn't expect, all while building a deeper relationship with Momo.
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 Kagome goes back in time and tries to change a major event in the past. For example, she might try to prevent a big battle that had a lot of casualties. She could use her modern knowledge and skills to her advantage in the past, like using first - aid knowledge to save lives.
Well, one possibility could be that Kurama goes back to a time when he was first captured by the shinobi. He might try to change things so that he doesn't end up in their hands initially. He could use his knowledge of the future to outwit his captors and escape much earlier, and perhaps even start a new life in a different part of the world.
Well, in the fanfiction, Itachi could go back in time and decide to train his younger self more rigorously. This would not only make him stronger but also change the way he approaches his future tasks. He might also try to influence Sasuke at an earlier age, guiding him in a different direction than in the original timeline. And he could befriend some characters earlier to build a stronger support network for the Uchiha clan.
Maybe Yusei goes back in time to prevent a great disaster that happened in the past. He could use his knowledge from the future to change certain events and save lives.
In a 'kaneki goes back in time fanfiction', perhaps Kaneki goes back to when he was still a normal college student. He then decides to study more about ghouls secretly. He could use this knowledge to try and find a way to co - exist peacefully between ghouls and humans from the very start. He might start by trying to change the views of some key people in the CCG, using his understanding of their future actions.
Well, one possible plot could be that Zuko goes back in time and tries to prevent the Fire Nation's aggression from the start. He could use his knowledge of the future to change things for the better, like trying to influence his father in a different way to avoid the war.
One possible plot could be Serena going back in time to prevent a major disaster in her world. For example, she might go back to stop an evil force from being released. In the past, she could meet younger versions of her friends and family, and they might not recognize her at first. She would have to use her knowledge from the future to try and change things for the better.