Naruto would probably be both amazed and a bit scared at first. But being Naruto, he would quickly jump into action. He might try to use his rasengan against Godzilla, thinking it could do some damage. However, he would soon realize that Godzilla is much more powerful than he initially thought and would have to come up with a different strategy, like using his speed to avoid Godzilla's attacks and find its weak points.
Naruto would be very curious about Godzilla. He would want to understand where it came from and why it was causing so much destruction. He might even try to befriend Godzilla in a way. He would approach it bravely, but also be cautious. He would rely on his instincts and his training as a ninja. He would also probably try to get his friends involved, like Sasuke and Sakura, to come up with a plan to deal with Godzilla together.
Most of the shinobi would be terrified at first. Naruto, being the curious and brave one, would probably be the first to approach Godzilla. Sasuke might be more cautious, seeing Godzilla as a potential threat. Sakura would be worried about the safety of the village. The older shinobi like Kakashi would try to analyze the situation and figure out how to deal with this unknown giant creature.
Some of them might be amused. For instance, Hulk could find it funny if Godzilla was shown as being weak in the fanfiction. He might laugh and say 'That big lizard not so tough!'.
Shinji would probably be terrified at first. He's already hesitant and scared in his normal battles, and Godzilla is much larger and more intimidating than the Angels he usually faces. Asuka would likely be more aggressive, thinking she can take on Godzilla with her Eva. Rei, on the other hand, would be very calm and observant, trying to understand Godzilla's nature. Misato would be in a panic initially, but then quickly start strategizing on how to deal with this new threat. Gendo would see Godzilla as either a new opportunity or a major obstacle depending on his long - term plans.
Ruby would probably be both scared and fascinated. She's always been curious about new things, and Godzilla is definitely something new. But she would also be worried about the destruction it could cause. Weiss might be more cautious and initially see Godzilla as a threat to the order in Remnant. Blake would likely be on guard, observing Godzilla's behavior to see if it's truly hostile or not.
Some of them would be amused. Hawkeye might chuckle at the outlandish scenarios in the fanfic. Black Widow would be more reserved but still interested. She'd be quietly observing and thinking about the implications of the story. Captain America would try to find the moral of the story, if there is one, as he always does.
Godzilla might see the pregnant Muto as a threat. After all, Mutos are his enemies. So he could start hunting it down to prevent more Mutos from being born.
He would probably be quite amused by some of his past antics. For example, his constant pranks on Iruka-sensei. But at the same time, he'd also see the pain he carried from not having his parents and realize how that influenced his actions. He might react with a bit of regret for some of the stupid things he did out of loneliness, but also be glad that those experiences made him who he is today.
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.