Another way could be that an ancient artifact in the Naruto world has some sort of connection to the Fairy Tail world. A character, like Sakura, touches this artifact and is instantly transported to the Fairy Tail world with amnesia. She is found by Natsu and his friends, and they are intrigued by her strange clothing and different powers. They start to investigate who she is while also protecting her from any threats in their world.
Perhaps in the Fairy Tail world, there's a forbidden spell that goes wrong. A Fairy Tail mage is trying to use it to reach a new dimension, which ends up being the Naruto world. When the mage arrives in the Naruto world, they lose their memory due to the instability of the spell. The first person they meet in Naruto is, for example, Sasuke, who is initially suspicious but then decides to help the amnesiac mage.
A crossover where a Fairy Tail mage ends up in the Naruto world with amnesia. The ninja initially suspect the mage is an enemy, but as they start to understand the mage's situation, they try to help. In the process, the mage discovers new types of magic by interacting with the chakra - based techniques in Naruto, and this new knowledge could potentially change the way magic works in their own Fairy Tail world once they return.
Naruto could save Fairy Tail in fanfiction through his strong will and never - give - up attitude. He has faced numerous challenges in his own world and emerged victorious. In the Fairy Tail universe, he could inspire the members of the guild to keep fighting even when all seems lost. He might teach them some of his ninja techniques which could give them an edge in battles. His experience in dealing with powerful and dangerous opponents would be invaluable in protecting Fairy Tail.
He could be a new addition to the Fairy Tail guild. As a baby, he'd bring a lot of innocence and new energy. The guild members would have to take care of him, like how they take care of each other. Maybe he'd be found near the guild's entrance one day, and they'd decide to keep him. His ninja abilities, even at a baby stage, might start to show in small ways, like his speed or reflexes, which could be interesting to the magic - using guild members.
First, decide on the main plot. It could be a simple idea like a character exchange between the two worlds. Then, choose which characters you want to focus on. For Naruto, it could be Naruto himself or Sasuke. From Fairy Tail, Natsu or Lucy might be good choices. After that, think about the setting. Will it be mostly in the Naruto world, the Fairy Tail world, or a mix? Once you have these basic elements, start writing an introduction that grabs the reader's attention, like starting with an action scene involving the main characters.
Mirajane could be a key character in a fanfiction where the worlds of Naruto and Fairy Tail are merging. Her strong magical powers would make her a valuable ally. In this merged world, she could help Naruto train to control new types of energy that are a combination of chakra and magic. She could also share Fairy Tail's sense of community and friendship with Naruto and his friends, which would strengthen their bonds and make them more united against any threats.
It could work by making Naruto a more mysterious and brooding character. In Fairy Tail, there are many characters with different personalities. An emotionless Naruto would stand out. He might be more focused on achieving his goals without being distracted by emotions. For example, he could be on a mission to find a way back to his own world and his lack of emotion helps him stay determined.
One way could be through a magical portal. Maybe a powerful mage in Fairy Tail accidentally creates a portal that links to the Naruto universe and Madara somehow gets sucked through it. Then he could use his powerful jutsu in the Fairy Tail world, creating all sorts of chaos and new storylines.
In a Naruto - Fairy Tail fanfiction where Naruto is a brother figure, he might bring a whole new dynamic. He could teach the Fairy Tail guild members some of his ninja training techniques. For example, how to better endure pain or how to focus their energy more effectively. Also, his backstory of being an outcast in his own village at first could make him relate to some of the Fairy Tail characters who have had difficult pasts.
Perhaps it's a matter of a powerful enemy from Fairy Tail's lore recognizing Naruto as a significant threat and using a very underhanded or extremely powerful attack on him. Since Naruto might not be fully aware of all the rules and powers in the Fairy Tail world, he could be caught off - guard. And in fanfiction, the writer might want to create a very dramatic and unexpected death for the sake of a unique story, so they come up with a scenario where Naruto dies in the Fairy Tail world.
In fanfiction, Naruto could become the founder of Fairy Tail by having his unique ninja skills and values influence the creation of the guild. Maybe he travels to the Fairy Tail world and decides to gather like - minded mages. His leadership skills, learned from being a ninja, would help him in setting up the guild's rules and training methods.