Well, his ability to see the future would likely cause a great deal of chaos. In the X - Man world, there are already so many complex relationships and power struggles. Harry's foresight could disrupt the balance. For example, he could see the rise of a new mutant threat and try to stop it in ways that the X - Men or the Brotherhood might not agree with. It could also lead to him being hunted by those who fear his power.
It might make his relationships more strained. For instance, if he sees a future where his friend gets hurt, he might become overprotective, which could annoy his friend. His friends might not believe him at first either, causing some friction.
His closest ally could be Professor X. Since Professor X is also very much about using his mental powers for good and has a great understanding of powers and how to control them. He would likely see the potential in Harry and help him develop his future - seeing ability further while Harry could use his ability to help Professor X in his plans for mutant - human coexistence.
This ability would make Naruto more cautious. Normally, he's quite impulsive, but seeing the future would force him to think before he acts. For example, if he sees that a rash decision leads to bad consequences in the future, he'll learn to hold back.
One possible plot could be that Harry Potter, with his newfound ability to see the future, teams up with the X - Men to prevent a major catastrophe. He might see a vision of a powerful mutant going rogue and causing destruction. The X - Men, with Harry's help, could then try to find and stop this mutant before it's too late. Harry could use his magic in combination with the mutants' powers to create unique strategies.
Well, it could make his relationships more complex. For example, if he sees a dark aura around someone, he might be more cautious. But if it's a bright, friendly aura, he could be more trusting. This ability would give him an extra sense when dealing with friends and foes alike.
Naruto's ability to see the future in fanfiction can really mess with his relationships. He could see a future where his friends die because of his actions. This would make him question his place among them and might lead to him isolating himself. With his family, like if he has a future vision about his kids, he might be overly strict or try to control their lives too much to prevent the bad things he saw from happening. And with his teacher, like Kakashi, if he sees a future where Kakashi is in danger, he may act impulsively to save him, which could cause problems in their normal teacher - student dynamic.
Well, initially, there would be some misunderstandings. The X - Men are used to dealing with mutants and their powers, while Harry is from a world of wizards. But as they get to know each other, they would start to interact more smoothly. Harry could use his future - seeing ability to warn the X - Men about upcoming dangers. The X - Men, like Wolverine, might be a bit skeptical at first but would soon come to trust Harry. Storm could be very interested in Harry's magic, and they could exchange knowledge about their different abilities. Cyclops, as a leader, would try to incorporate Harry into their plans based on his visions.
If Naruto sees a future where he and Sakura are not as close as they are in the present, he might start to distance himself from her, thinking it's for the best. Or on the other hand, he could try to change the future by being more open and communicative with her. Also, with Sasuke, if he sees a future where Sasuke is in more danger than he thought, he would redouble his efforts to keep Sasuke safe and this would likely deepen their complex relationship.
Naruto's future - seeing ability could completely shift the power balance in the story. He could use it to find out where all the powerful artifacts or secret techniques are hidden in the future. For instance, if he saw the location of the Sage of Six Paths' hidden power, he could get there first and gain that power. This would put him in a much stronger position than his opponents, and might even change the political situation in the ninja world as different villages would react to his new - found strength.
Well, it could change the plot in many ways. For example, the crows might act as spies for Harry, giving him information about the Death Eaters' whereabouts. They could also help him find hidden objects or secret passages. Maybe they warn him of impending danger.