He might be really surprised. He would see all kinds of new interpretations of his world, his friends, and his adventures. Some fanfics could show him achieving even greater things in the future, which would make him feel proud. And if there are fanfics that explore his relationships in new ways, he'd be quite intrigued.
Since Naruto is an adventurous person, he would be eager to explore the different scenarios presented in future fanfic. He would be open - minded about new ideas like new jutsu or different relationships between characters.
There would likely be a lot of negative reactions. Fans of the Naruto series who love the original themes of friendship, heroism, and ninja values would be appalled. The Naruto fandom is quite large and protective of the original spirit of the show, so this kind of fanfic would be seen as a desecration of the characters and the world that has been created.
Naruto would probably be deeply hurt. He values his relationship with Sasuke so much that such a betrayal would shatter him. He might become withdrawn or angry.
In Naruto future reaction fanfiction, characters might react to various things. For example, they could react to new jutsu developed in the future. They might be amazed at the power and creativity behind it. Maybe Naruto himself would be excited to see how the next generation has advanced the art of ninjutsu.
He might be shocked. In the fanfic, if he sees things like his friends' future achievements or the new threats that emerge, it would surely startle him. For example, if he discovers that one of his friends has a family of their own and has become a great leader in the village, he would be proud but also a bit surprised at how much has changed.
Hinata would probably be extremely shy at first. She might blush furiously and be at a loss for words. After all, she has had a crush on Naruto for a long time, so it would be a dream come true for her.
Most of the fandom would probably be horrified. Naruto is known for his positive values, and killing a family member is completely against that. There would likely be a lot of criticism towards the author of such a fanfic.
A frequent theme is the exploration of character relationships in the future. For instance, how do Naruto and Sasuke's relationship evolve further? And how do other characters react to this? Also, the theme of facing new, more powerful threats together often appears. Characters' reactions to these threats can vary from determination to fear.
They might be shocked. They would see things they never expected, and it could change their view of the future. Maybe they'd be excited to see positive changes or worried about potential disasters.
He could be instantly fascinated. Howard Stark has a love for all things new and innovative. When presented with the future in fanfiction, his eyes would widen with excitement. He'd start asking questions, trying to figure out how things work. He might even start scribbling down ideas on how to bring some of those future concepts back to his own time, regardless of how impossible it might seem at first.