Naruto's reaction could be complex. On one hand, he would be happy to find someone else from his clan. He has always been proud of his Uzumaki heritage despite not knowing much about it at first. But on the other hand, he might be a bit cautious. Karin has been associated with some not - so - good groups in the past. However, overall, his positive nature would probably lead him to approach Karin with an open mind and try to build a connection with her based on their shared Uzumaki roots.
Naruto would probably first try to find a peaceful solution. He has always been one to believe in the power of friendship and understanding. He might try to talk to the leaders of both villages, like Gaara in the Sand, to find out what's really going on and resolve the misunderstandings.
He is probably very excited. Naruto has always been eager to learn new things and become stronger. Finding an Uzumaki scroll means he has the chance to discover something unique about his own clan, so he would be filled with anticipation.
At first, Naruto might be shocked and confused. He would probably wonder why his own clan would do such a thing to him. He might feel a deep sense of betrayal, especially since he has always longed for a family and a sense of belonging within the Uzumaki clan. But being Naruto, he would soon turn his confusion and pain into determination. He would vow to prove himself and show the clan that they were wrong to exile him.
A villain like Shigaraki would likely be interested in the power levels in the MCU fanfiction. He's always looking for ways to increase his own power, and seeing the various powerful artifacts and abilities in the MCU might give him some ideas. He could think about how he could use similar things in his own plans to take over the MHA world.
The Legend of Uzumaki Hiroto was a derivative work of Naruto, which told the story of Uzumaki Hiroto's growth and the stories of other characters. Uzumaki Boto Legend was different from the original Naruto Naruto Shimbun Legend, so it was considered an independent manga.
It depends on the specific plot of the fanfic. Sometimes he could be on a secret mission, in a hidden village, or facing a new challenge in an unknown location.
Some MHA characters might be flattered. For example, Midoriya would probably be really excited and take it as a sign of how much he's inspired people. He might even look for positive lessons in the fanfiction to improve himself.
If the MHA characters were to react to a Mastermind fanfiction, some would be more accepting than others. Characters like Ochaco might find it really exciting. She's a fan of the heroes herself, so seeing different takes in fanfiction would be like getting a new perspective on the MHA world. However, characters like Shoto, who are more reserved, might be a bit hesitant. He might need some time to process what he's reading. But overall, it would be a very interesting scenario as it would show how the characters view different interpretations of their world.
Some characters would be shocked. For example, if the fanfiction had a really dark and unexpected Mastermind plot, like a hero turning out to be the mastermind of all the villains' plans, characters like Tsuyu would be very taken aback. She'd probably question the motives behind such a plot. Then there are characters like Denki. He might be more into it if it had some cool action scenes in the fanfiction, regardless of how out - of - the - blue the Mastermind storyline was. And Nejire would probably be super curious about the emotional depth of the characters in the fanfiction.