Naruto would probably have a range of reactions. He could be excited to see new adventures that people have written for him. But if the fanfiction was inaccurate about his character, like making him cowardly when he's known for his bravery, he would likely be a bit miffed. He might also be curious about the new relationships with other characters that the fanfiction presents.
Naruto's reaction would depend on the nature of the fanfiction. If it was positive and showed him achieving great things in the future, he'd probably be happy and maybe even a bit motivated. But if it was negative, he'd be disappointed. For example, if it showed him failing to protect his loved ones. He would also be fascinated by the creativity of the writers, especially if they came up with new powers or abilities for him that he hadn't thought of before.
He would likely be very curious. Naruto has always been eager to learn and explore new things, so seeing future fanfiction would be like opening a door to a new world of possibilities for him.
Naruto might react with a sense of responsibility. If he saw a future where Konoha was in danger, he would feel it was his duty to do something about it. He could start by gathering information from the future vision, like the weaknesses of the enemy. Then, he would share this knowledge with his comrades and come up with a plan to protect the village.
Some of them might be shocked. Tony Stark, for instance, might immediately start thinking of ways to use technology to change what he saw. Steve Rogers would probably be more concerned about the moral implications of interfering with the future.
They might be confused at first. Fanfiction can be wild and different from their real experiences.
Minato and Kushina would likely have a complex reaction. They would be proud of Naruto's heroic deeds in fanfiction. But if they saw him being in danger or having a hard time, they would be worried. Also, if there are parts where Naruto's values seem different from what they taught him, they might be a bit confused.
He might be really surprised. Naruto is used to his own world and the fanfiction could show things he never imagined. For example, if the fanfiction has his kids achieving great things in new ways, he'd be proud yet a bit shocked at how creative fans can be.
He might be shocked at how the village has developed. In some fanfictions, the village could have advanced technology. Naruto, being from a more traditional ninja world, would likely be both amazed and a bit confused at first.
He might be shocked at first. In fanfiction, the future could be full of unexpected changes. He could be excited to see how his friends and the village have developed. Maybe he'd be a bit sad if things didn't turn out as he hoped for his loved ones.
Some characters might be shocked. For example, Naruto himself would probably be really excited to see how his world is imagined in the future. He'd be happy to see that his story has inspired so many different ideas. Sasuke, on the other hand, might be a bit more skeptical. He'd analyze the fanfiction carefully, looking for any inaccuracies or misinterpretations of his character or the ninja world's values.
They may find it funny. There are often humorous fanfictions that could make them laugh.