At first, Naruto would probably be really confused. The fanfiction world is often a wild place with all kinds of interpretations. But then he might start to see the charm in it. He could find fanfictions that give his friends more backstory or depth that he didn't know before. He might also come across some really wacky ideas that make him laugh. However, he might also be a bit defensive if the fanfiction goes against his values or the way he sees his relationships in his own world.
He might be surprised. He's used to his own life and adventures, and seeing it twisted and turned in fanfiction could be unexpected.
Naruto might have a mixed reaction. He could laugh at the funny parts of the fanfiction. However, if the fanfiction misrepresents his friends or his village in a negative way, he might get angry. He's very protective of those he cares about. He may also be intrigued by the different versions of himself that are presented in the fanfiction, and might even start to think about how he can grow in those new directions.
Sakura would probably tease Naruto a little bit. She might say something like 'Naruto, you're such a dork for reading that fanfiction.' But then she would also be interested in what it's about and might ask Naruto to tell her some of the cool parts.
Sakura might tease Naruto about it a little. She'd probably think it's a bit strange that he's interested in something so different from their own world. But she'd also be curious to know what it's all about.
Naruto would be very curious. He'd want to understand what's going on. Once he figures out that there's a big battle between different factions, he'd try to find a peaceful solution. He might start by talking to the leaders, using his charm and persuasion skills. If that doesn't work, he'd use his ninja powers to protect the innocent. He's not one to just stand by when there's injustice.
He would probably be very confused at first. Naruto has always trusted Tsunade, so the betrayal would come as a huge shock.
Naruto would probably be very surprised. He has heard about Rin from Obito and Kakashi. So when he actually meets her, he might be at a loss for words at first.
He would be heartbroken. Naruto values friendship above almost everything. At first, he might not believe it and try to reason with his friends.
At first, Naruto's eyes would widen in surprise. He'd pick up the fanfiction, not really knowing what he's getting into. As he starts to read, he'd be constantly muttering things like 'What the heck?' and 'This is so strange!'. He might try to find someone to explain it to him, but if no one could, he'd likely just shrug it off as something he doesn't need to understand.
He could initially go into denial. Naruto has always been an optimist. He might not be able to believe that his wife, the person he loves, could betray him. But once the truth sinks in, he would start to analyze the situation carefully. He might try to find a way to redeem her, depending on the nature of the betrayal, as he always believes in the power of forgiveness and second chances.
At first, Naruto would be completely shocked. He has always seen Hinata as a loyal friend and someone who has deep feelings for him. So the idea of her betrayal would be hard to fathom. He might try to deny it at first.