Lucy could be a likely candidate. She is a Celestial Spirit mage, and there could be some connection between her magic and seeing the future through her spirits. For example, maybe one of her spirits has the power to grant her glimpses of the future. Another one could be Jellal. Given his complex backstory and powerful magic, it's possible that in fanfiction, he could develop or already have the ability to see the future as part of his evolution or redemption arc.
Lily Potter would also be involved. She was James' wife, and if James saw something in the future that affected their family, he would surely involve her. Also, Dumbledore might be in the story. He was always a key figure in the wizarding world, and James might seek his advice on what to do with his visions of the future.
Obviously, Naruto would be the main character since it's about his past seeing the future. Sasuke would also be important as Naruto's relationship with him is central to the Naruto series. Kakashi too, as he is Naruto's teacher and mentor, and his guidance might be influenced by Naruto's new - found knowledge of the future.
One interesting idea could be how the characters use their knowledge of the future to prevent disasters. For example, if Natsu knew that a powerful dark guild was going to attack Magnolia in the future, he might train harder or seek out new powers to stop it. Another idea could be the moral dilemmas that come with seeing the future. If Lucy saw that a friend would die in a future battle, would she try to change it even if it meant disrupting the natural order? And perhaps some fanfictions explore how seeing the future affects the relationships between the characters. Maybe Gray, who has always been a bit reserved, becomes more open and protective of his friends when he realizes what could happen to them in the future.
Naruto is the central character, no doubt. Hinata could be important as well. If Naruto sees a future related to his family or his relationship with Hinata, she will play a significant role. Additionally, the Hokage, like Tsunade or whoever is in charge at that time, would be important as Naruto may need to report the future he saw to the village leadership to take collective action.
Hinata would also be highly affected. She has always admired Naruto from afar. By seeing his memories, she would understand him on a whole new level, his struggles, his hopes, and it would likely strengthen her feelings for him even more. And it could also change how she interacts with him in the story.
One character that would likely have a different role is Sirius Black. In an alternate universe, he might not have been wrongly imprisoned, and he could be a full - time mentor to Harry. Luna Lovegood could be a more powerful and influential figure in the wizarding world. And Voldemort himself could be a reformed wizard, which would turn the whole story upside down.
Obviously, Natsu would be one of the main characters. He's always at the center of things in Fairy Tail, and seeing the future would surely lead him into some wild adventures.
Peter is obviously one of the main characters since it's about him seeing the future. His friends, like Ned and MJ, often play important roles too. They could be the ones Peter is trying to protect or they could help him deal with the visions.
Gray is another candidate. Gray's cool and collected demeanor could contrast with Tobi's more mysterious nature. They could get into arguments about the best way to handle a situation, like when facing a powerful enemy. Or, they could find common ground in their skills and work together to protect Fairy Tail from danger.
It could be a new character, perhaps someone from a far - off land who has a grudge against Naruto's future self for some reason. This character might be extremely powerful and has plans to destroy everything Naruto holds dear. When Naruto sees this future, he has to find a way to stop this new threat before it even begins to form.