Maybe Natsu hates Fairy Tail fanfiction because he doesn't like how some fanfictions distort the original story or the characters. In the original Fairy Tail, he has a clear personality and relationships, and fanfictions might change that in ways he wouldn't like.
Sure, there may exist such fanfictions. In the official 'Fairy Tail' story, Natsu and Lucy are very close. But fanfiction is a world of creativity and deviation from the original. A writer might decide to make Natsu hate Lucy due to some made - up reasons like a misunderstanding or a conflict of interests. This could lead to a whole new set of adventures or conflicts within the 'Fairy Tail' universe as rewritten by the fanfiction author.
One reason could be that the fanfictions don't match his view of the Fairy Tail world. He has his own understanding of the guild, his friends, and their adventures, and when fanfictions deviate from that, he doesn't like it.
Well, it could mean that in a Fairy Tail fanfiction, the character Natsu is depicted as having feelings of hatred. Maybe the author of the fanfic has created a scenario where Natsu hates something specific like a particular character, a situation, or an event within the context of the Fairy Tail universe.
Well, in some fanfictions, Natsu might hate a certain type of mission. For instance, if it involves working with a group of people he doesn't trust. Or perhaps there is a fanfic where Natsu hates a new law or rule that has been imposed in the Fairy Tail world. This rule could be restricting the freedom of the guild members, and Natsu, being a free - spirited character, hates it. There could also be a fanfic where Natsu hates a powerful object that has a corrupting influence on the people around him.
It would change the dynamic of the team. Usually, Lucy and Natsu are good friends and partners. If she hates him, their teamwork would be affected. They might not be able to fight enemies as effectively. For example, when facing a strong opponent that requires their combined magic, they might not be able to synchronize well.
Yes, in a lot of Fairy Tail fanfiction, Natsu can be overpowered. Writers often like to amp up his powers for more exciting storylines. For example, they might give him new fire - based abilities or make his existing ones even stronger to defeat more powerful foes.
In fanfiction, Natsu's age can vary greatly. Some authors might keep him at his canonical age from the original Fairy Tail series, which is around 17 - 18 years old at the start. However, in alternate universe fanfictions, he could be older or younger depending on the plot. For example, in a time - travel based fanfic, he could be much older if the story takes place far into the future or much younger if it goes back to his childhood days.
It could be that the characters in Naruto have a distinct personality and world - view that don't mesh well with the Fairy Tail universe in fanfiction. For example, Naruto's values of hard work and friendship in his own ninja world are different from how they might be portrayed when forced into the Fairy Tail setting. Fans who are loyal to Naruto's original concept might hate seeing it distorted in Fairy Tail fanfiction.
Mostly, it's hard to find solid evidence. It could be just a vocal minority within the 'Fairy Tail' fandom who feel this way. There's no official statement from the creators of 'Fairy Tail' or any large - scale surveys showing that the entire 'Fairy Tail' fan base hates 'Naruto' fanfiction. It could also be that this statement is an over - generalization of some sporadic negative reactions.