The power scaling might be another issue. Naruto has a very detailed and complex power system that is based on chakra, jutsu, and ninja ranks. Fairy Tail has its own magic - based power system. In fanfics, getting these power systems to mesh well can be difficult, and Naruto might 'hate' being part of a poorly - balanced power - system fanfic.
Perhaps the art styles play a role. Naruto has a distinct art style that some people are really drawn to, and when they look at Fairy Tail, they just don't like the visual aspect as much. Also, the story themes in Naruto are often darker and more about political intrigue and personal sacrifice, while Fairy Tail is more about friendship and adventure. Fans of Naruto's darker themes might not like Fairy Tail's more upbeat nature.
Perhaps he thinks fanfic undermines the integrity of the original Naruto story. The official story has a certain narrative and character development, and fanfic can deviate from that significantly. When it comes to his connection with Naruto, any deviation in fanfic might be seen as a negative. For example, if a fanfic changes the way he mentors Naruto, it could be something he wouldn't like.
Maybe Naruto hates Fairy Tail fanfic because the two universes have very different themes and power systems. Naruto's world is more about ninja skills, clan politics, and personal growth within a set ninja framework. Fairy Tail is about magic guilds and more flamboyant magic use. The clash of these different concepts in a fanfic might be unappealing to Naruto fans who prefer the purity of the Naruto universe.
One possible reason is the difference in power systems. Naruto has its chakra - based ninja abilities, while Fairy Tail has magic. Combining them in fanfiction might seem forced and not make logical sense to fans of Naruto.
Another reason could be that the Rookie Nine have different goals or values that conflict with Naruto's. For instance, if they are more focused on self - interest rather than the greater good that Naruto is always striving for. This divergence in values might lead to Naruto's dislike and eventually hatred for them. And also, personal conflicts within the group that Naruto gets caught in the middle of could be a factor.
Maybe there is a misunderstanding. Since it's a crossover fanfiction, communication between the two different worlds' characters might be difficult. So, Naruto could be misjudged and betrayed because of false assumptions.
One reason could be that some fans are very purist about the original Naruto story. They might feel that fanfiction often distorts the characters or the plot in ways that go against the essence of what Naruto is all about. For example, changing a character's personality completely to fit a romantic or dark and edgy narrative that doesn't align with the source material.
In a fanfiction, there could be a situation where Lucy is forced to side with a group that Natsu is against. This would make Natsu see her as an enemy. Or perhaps there is a prophecy that Lucy is involved in that Natsu misinterprets as something bad. He might think she is a threat to the guild or his friends. Also, if there is a love triangle situation where Lucy chooses someone else over Natsu in a way that really hurts his feelings, that could be a reason for him to start hating her.
The different power scales. Naruto has his own progression of power through training and ninja ranks. Superman's power is on a completely different level like being able to move planets. In fanfiction, it might be hard to balance their powers in a way that makes sense to Naruto fans, so Naruto might seem to 'hate' it.
Perhaps in fanfiction, Boruto is associated with a group or ideology that Naruto opposes. This could cause Naruto to view Boruto unfavorably. Also, if there are false rumors or misinformation spread in the fanfiction world about Boruto, Naruto might believe them and start to hate Boruto until the truth is revealed. And sometimes, it's just a way for the writer to make an interesting and unexpected plot twist.