One idea could be a crossover where a powerful Naruto villain somehow ends up in the Fairy Tail world and causes chaos. The Fairy Tail mages would have to use their unique magic to combat the ninja - like abilities of the Naruto character.
A really interesting plot could be that the magic in the Fairy Tail world and the chakra in the Naruto world are actually related in some ancient way. A group of characters from both worlds, including Naruto characters and Fairy Tail mages, team up to uncover this mystery. Along the way, they face challenges from those who want to keep this secret buried.
A plot could involve a powerful dark force threatening both the Naruto and Fairy Tail universes. This force could be something that neither ninjutsu nor magic can easily defeat. So, the characters from both worlds must come together. The GMG could be a platform where the first interactions occur. Maybe some Naruto characters enter the GMG under false pretenses to investigate this new threat that seems to be related to the event.
One idea could be that Naruto characters end up in the Fairy Tail world and have to participate in the Grand Magic Games. They could show off their ninja skills which would be a novelty there. Another could be a team - up where Fairy Tail mages and Naruto ninja join forces to fight a common enemy that threatens both their worlds, like an ancient evil that can travel between dimensions.
One idea could be that the Fairy Tail guild travels to the Naruto world somehow. They could team up with the ninja to fight a common enemy like a powerful dark magic user who has also invaded the ninja world. Maybe Natsu's fire magic could be compared and combined with Sasuke's fire jutsu in some unique ways during battles.
Maybe there could be a plot where a powerful villain from the Naruto universe, like Orochimaru, teams up with a dark mage from Fairy Tail. The combined threat forces the heroes from both worlds to work together. The Fairy Tail members would be amazed by the unique abilities of the ninja, like Sasuke's Sharingan and its various powers. In turn, the Naruto characters would be intrigued by the wide array of magic in Fairy Tail, such as Erza's Re - Quip magic.
One idea could be a crossover where Naruto characters learn magic from Fairy Tail. For example, Naruto might learn fire magic and combine it with his Rasengan. Another idea is that the guilds in Fairy Tail and the villages in Naruto have to team up to fight a common enemy, like an ancient dark force. And perhaps some of the Fairy Tail wizards could teach the ninja in Naruto about the power of friendship and how it can enhance their abilities.
One idea could be that Naruto somehow ends up in the Fairy Tail world and is mistaken for a powerful wizard. The female characters in Fairy Tail start to develop feelings for him due to his unique ninja skills and kind heart. For example, Lucy might be intrigued by his ability to summon shadow clones and see it as a form of celestial spirit magic. Another plot could involve a magical artifact that links the two worlds, and Naruto and the Fairy Tail characters have to work together to protect it from a common enemy. This would bring them closer and lead to the development of a harem situation as the female characters from both universes start to fall for Naruto.
Maybe in the fanfiction, there is a magic spell that fuses Naruto and Wendy's powers together. This new power is needed to defeat an ancient evil that is awakening. They have to learn to control this combined power and also deal with the cultural differences between the ninja world and the Fairy Tail world. For example, Naruto is used to stealth and quick strikes, while Wendy is more accustomed to magical battles in open areas.
A simple yet interesting plot could be a race. The White Dragon could be part of a race in the Fairy Tail world, and some Naruto characters get invited. Naruto, with his speed and determination, could compete against the White Dragon and other Fairy Tail mages. It would be a test of different powers and abilities.
Another plot idea is that Lucy, while on a mission, discovers a strange magical artifact that has a connection to Naruto's world. She accidentally activates it and it summons Naruto. Together, they have to figure out how to send Naruto back while also dealing with the chaos that the artifact's appearance has caused in the Fairy Tail guild. For example, it could be causing some of the guild members to have strange powers or behaviors similar to those in Naruto's world.
A possible plot is that Naruto is mistaken for a powerful wizard in the Fairy Tail world. Erza initially doubts him but as they get into battles together, she realizes his strength. They have to work together to stop a ancient evil that is awakening. Along the way, Naruto's positive attitude starts to change the way the Fairy Tail guild members view things, and Erza becomes more open - minded due to Naruto's influence.