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, Harry Potter himself could be involved. He might be a mentor figure in the future, passing on his knowledge and experiences to the new generation. His children, if the fanfiction extends to that, would also be key characters. Hermione and Ron could also play important roles, perhaps as educators or as important figures in the wizarding government. Neville Longbottom could be involved too, maybe as a herbology expert who is helping to develop new magical plants for the future wizarding world.
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.
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.
Hermione Granger is also a likely character. Her intelligence and love for knowledge could lead her to discover a way to bridge the past and the future. She might use her Time - Turner knowledge or find some new magical method. And she could play a key role in helping past characters adapt to the future or vice versa.
Well, it could be that James Potter sees the future and tries to prevent a great tragedy from befalling the wizarding world. Maybe he sees Voldemort rising to power earlier than expected and he has to figure out a way to stop it without changing too much of the future.
The main characters are Naruto and his comrades. Iruka, Naruto's first teacher, could be in it too. He has always been like a father figure to Naruto. In the fanfiction, he might be one of the first to notice something strange about Naruto's future. Then there are Naruto's other friends from the village like Kiba and Choji. They would all react differently to seeing Naruto's future. Kiba might be more impulsive in his actions to change it, while Choji might be more cautious but still determined to help Naruto have a better future.
Obviously, Harry Potter himself is the central character as the one being abused and neglected. The Dursleys are also key characters as they are the ones who abuse and neglect him in the original story. Hermione and Ron might also be involved as they could be the ones to discover Harry's situation and try to help him. Dumbledore could also be a part of it, perhaps as someone who failed to notice or prevent Harry's abuse initially.
Obviously, Harry Potter himself. Hermione would probably be by his side, helping him research about his claim to lordship, using her vast knowledge from the library. Ron might also be there, providing moral support and his unique sense of humor in difficult situations.
Harry Potter himself is obviously a central character as the focus of the so - called 'harem'. Hermione Granger could be one of the likely characters involved. She is Harry's close friend in the original series and her intelligence and magical abilities would make her a strong contender in any relationship - based competition. Ginny Weasley is also a likely character, as she has a romantic relationship with Harry in the official story. Luna Lovegood might be included too, with her unique personality and magical insights.
Snape is a likely candidate. In the original series, his loyalties were always a bit of a mystery at first. In fanfiction, he could be further explored in terms of false betrayals or real ones. Another one could be Draco Malfoy. He was on the verge of becoming a full - blown Death Eater in the original, so in fanfiction, he could either truly betray his Hogwarts classmates or be wrongly accused of betrayal.