Another reason might be related to Naruto's loyalty being questioned. In fanfiction, there could be a plot where an enemy tricks the guild into believing Naruto has betrayed them. The Fairy Tail guild values loyalty highly, and if they think Naruto has sided with an enemy, they might banish him. For example, if an enemy uses some sort of illusion magic to make it seem like Naruto has attacked a guild member, this could lead to his banishment.
It could also be due to internal guild politics. There might be some members who are jealous of Naruto's popularity or his rapidly growing power within the guild. They could spread false rumors or manipulate situations in such a way that the guild leadership decides to banish Naruto. In a fanfiction scenario, perhaps some long - established guild members feel threatened by Naruto's new - found status and push for his removal.
Naruto would likely be very confused at first. He has a strong sense of belonging and has always fought for his place in his own ninja village, so being suddenly banished from the Fairy Tail guild would be a shock. He might try to plead his case and explain that he has done nothing wrong.
One possible reason could be that he was wrongly accused of a serious crime within the guild. Maybe some powerful and influential members believed he was a threat and pushed for his banishment. For example, if there was a string of mysterious attacks and Natsu was framed as the culprit due to his often wild and uncontrollable nature in battle.
Maybe in the fanfiction, there were some political motives. Hiruzen might have been pressured by other hidden villages. They could have threatened Konoha if Naruto, as the Nine - Tails' jinchuriki, remained in the village. So, to avoid a potential war or conflict, Hiruzen made the difficult decision to banish Naruto. Also, it could be due to a misunderstanding. Naruto might have been in the wrong place at the wrong time during an incident, and Hiruzen misjudged the situation.
One possible reason could be for the protection of the village in a very extreme and controversial way. Minato might think that Naruto's presence is attracting too much danger and decides to banish him to keep the village safe.
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 possible reason could be false accusations of a serious crime. For example, if he was wrongly blamed for a major attack on the village. Another reason might be political intrigue. Some powerful figures in the village might see Naruto as a threat to their power and find a way to banish him to maintain their control.
One possible reason could be that she is wrongly accused of a serious crime she didn't commit. For example, if there was a major theft in the village and false evidence was planted against her. Another reason might be that she has some new and powerful abilities that the village elders fear. They may think she could become a threat in the future, so they banish her to protect what they see as the village's stability.
One possible reason could be a sense of adventure. Romeo might feel that the guild has become too stagnant for him and he wants to explore new lands and face new challenges on his own. In fanfiction, authors often like to take characters out of their comfort zones to develop them further.
Well, perhaps in this fanfiction, Naruto is banished due to a false accusation in his world. He lands in the Fairy Tail world and is seen as an outsider. However, his determination and strong will attract the attention of some of the Fairy Tail members. Erza, for example, might see his potential and take him under her wing, training him in the ways of the Fairy Tail magic while he also teaches her some ninja tricks.
One possible reason could be that Naruto discovers some dark family secret that his parents want to keep hidden. For example, if there was a connection between the Uzumaki clan and some forbidden jutsu, and they fear Naruto might be exploited because of it. So they banish him to protect the clan's reputation and his own safety.