One possible reason could be a conflict of power. Naruto has his own set of powers from the Naruto universe, like chakra and jutsus. In Fairy Tail, magic is the main power source. Maybe his powers were seen as a threat or too different, causing the guild to force him out. For example, if his chakra-based attacks were disrupting the magical balance in Fairy Tail's world.
The overall mood of the story would change. It would become more somber. There would be a sense of loss. And it might lead to a quest to bring Naruto back. Maybe some of the Fairy Tail members would go on a journey to prove Naruto's innocence or to find a way to make the guild accept him again. This would open up new story arcs and adventures in the fanfiction.
It could lead to a change in the guild's dynamics. Naruto has his own unique combat style and abilities. His departure might make the guild realize the need to diversify their fighting strategies. For example, they might start to look for members with skills similar to Naruto's ninja techniques.
Maybe it's due to power differences. Naruto has his own set of unique and powerful jutsu. In the Fairy Tail universe, magic is the main form of power. He could feel that his powers are not being utilized or respected in the right way. He might also be frustrated with the lack of understanding of his ninja skills among the Fairy Tail members, so he chooses to leave.
Well, in such a fanfiction, Naruto might bring his unique ninja skills to Fairy Tail. His shadow clone jutsu could be used in creative ways during battles in the Fairy Tail world. Maybe he'd form an interesting bond with Natsu, sharing their love for a good fight and loyalty to their friends.
It could be about the deep bonds and loyalty within the 'Fairy Tail' universe in the context of fanfiction. Maybe it focuses on characters making a solemn vow not to leave each other, which is a common and powerful theme in 'Fairy Tail' as the guild members are like a family.
In this fanfiction, Naruto would likely develop a new sense of family. Fairy Tail is known for its strong sense of community and family - like bonds. Naruto, who has always craved family and friendship, would thrive in this environment. His character would grow to be more empathetic as he experiences the various plights of his new Fairy Tail comrades. He might also start to use his skills in more strategic ways, learning from the battle - hardened members of Fairy Tail.
He could leave because of a misunderstanding. Maybe he overhears something wrong and thinks the guild doesn't trust him or value him anymore. So in a fit of anger and pride, he decides to leave.
A possible reason could be personal conflicts within the guild. Lucy might have an issue with some of the guild's rules or how certain things are run. Juvia could be following Lucy for some reason, like loyalty or because she also has her own issues with the guild. For instance, if there are tensions between Juvia and other members over Gray.
Maybe they leave because they want to search for answers about their pasts. Happy might want to know more about his origins, and Lucy could be seeking something related to her family's history.