You could make an OC guild that is a rival to Fairy Tail at first but then has to team up with them to face a common enemy. The OC in this guild might have a grudge against Fairy Tail initially because of a misunderstanding. For instance, they think Fairy Tail stole a powerful magic artifact from their guild long ago. But as they work together, they realize that they were wrong and form strong bonds with the Fairy Tail members.
He could be the new rising star. He might start off as a bit of an outcast because he's new and has different ways of doing things. But as he shows his strength and loyalty, he quickly becomes an important member. For example, he could be the one to solve a really difficult mission that the guild has been struggling with, earning everyone's respect.
The guild as a whole would likely mobilize. Erza would start formulating a strategic plan. She'd consider the strengths and weaknesses of Acnologia and figure out the best way to approach the situation. Gray would also be ready to fight, using his ice - make magic to support the rescue mission. They would all be united in their determination to get Lucy back safely.
The Fairy Tail guild would probably be very curious about Naruto at first. They might be amazed by his strange abilities like running up walls and creating clones. Some members, like Lucy, would likely be a bit cautious, but also intrigued. Natsu would probably be eager to test his strength against Naruto right away.
Pay attention to the world - building. Expand on the Fairy Tail universe. Describe new locations, cultures, and magic rules that are relevant to your OC guild. You could also include references to Fairy Tail's history in a new and interesting way. For example, your OC discovers a long - lost spell that was once used by the founders of Fairy Tail, and this discovery changes the course of the story in a big way.
Another great choice could be Laxus. He has that tough - guy exterior but also a lot of room for character growth. In a fanfiction as guild master, he could bring a different leadership style, more aggressive perhaps. He might change some of the guild's traditions while still maintaining the core values of Fairy Tail. He also has a great relationship with his team, which could be further developed in the fanfiction.
If Sasuke joined a Fairy Tail guild in fanfiction, there would be a lot of drama. The other guild members would be initially suspicious of him because of his cold and brooding nature. But his skills would quickly earn him respect. He might have a hard time adjusting to the guild's more laid - back and friendly atmosphere compared to the ninja world. However, his determination to become stronger would fit right in with Fairy Tail's spirit.
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.
One possible fanfiction could be about a character from Naruto being transported to the Fairy Tail universe and getting involved with a Dark Guild. Maybe Naruto's skills in combat and his never - give - up attitude would help him either infiltrate the Dark Guild to gather information for Fairy Tail or try to reform some of the members.
Sakura could fit in as a healer. In Fairy Tail, having a powerful healer is always valuable. Her medical ninjutsu skills would be highly regarded, and she could quickly become an important member of the guild when it comes to treating injuries after battles.