One possible plot could be that the Akatsuki from Naruto Shippuden somehow gets involved with the dark guilds in Fairy Tail. For example, they could form an alliance to steal powerful magical and ninja artifacts. Naruto and his friends, along with the Fairy Tail members, would then have to team up to stop them. They could start off being suspicious of each other, but as they face common enemies, they learn to trust and use each other's unique abilities.
One great Naruto Shippuden fanfiction could be those that explore alternate endings to the series, like what if Sasuke never left the village. For Fairy Tail, fanfictions that focus on the backstories of the guild members can be really interesting. For example, a story about how Makarov founded the guild in more detail.
Well, Naruto's Rasengan could potentially interact with Natsu's Fire Dragon's Roar. The Rasengan is a concentrated ball of chakra, and if Natsu were to blast his fire at it, it could either be deflected or the two powers could combine to create a more powerful attack. Also, Sasuke's Sharingan could be used to analyze the magic spells of Fairy Tail wizards. He could then predict their moves and counter them more effectively.
You can start by checking out popular fanfiction websites like FanFiction.net and Archive of Our Own. They have a large collection of fanfictions for both series. Just search for 'Naruto Shippuden' and 'Fairy Tail' separately or together if you're interested in crossovers.
In that fanfiction, it might be designed that way. Naruto has incredible powers in his own series, like his various jutsu. If translated into the Fairy Tail world in fanfiction, his skills could potentially make him very powerful. But it also depends on how the author of the fanfiction interprets and balances the power systems of both universes.
The Sharingan in such a fanfiction could be used as a tool for a Fairy Tail character to gain an edge in their battles. They might initially struggle to control it, but as they learn more about it, they become a formidable force. For instance, they could use the Sharingan's genjutsu abilities to deceive opponents in the Fairy Tail battles.
In the Fairy Tail world, Naruto would bring his unique ninja abilities. For example, his shadow clone jutsu could be used in creative ways during battles or to perform tasks. He would likely befriend Natsu because they both have a passion for fighting and protecting their friends. Naruto could also introduce new combat styles to the Fairy Tail guild, which might change the way they approach battles.
Well, Naruto would probably gain some really unique magical abilities. Fairy Tail mages are known for their diverse magic, and Naruto could combine his chakra skills with something like Fire Magic or Celestial Magic. He might become even more powerful in combat, with new ways to attack and defend.
Well, Naruto's ninjutsu skills would be quite a novelty in the Fairy Tail world. His shadow clone jutsu could be used in some really creative ways during battles, like overwhelming opponents with a large number of clones. Team 7 as a whole would bring a different dynamic. Sasuke's sharingan could give them an edge in detecting magic and illusions. Sakura, with her medical skills, could be a great asset in treating wounded mages. And Kakashi, with his experience and wide range of jutsu, would be like a mentor figure to the Fairy Tail members, teaching them new strategies.
In a Naruto - Fairy Tail - Mirajane fanfiction, it could start with Mirajane traveling to the Naruto universe. She might be on a quest to find a special kind of magic that she believes exists there. When she arrives, she meets Naruto. Naruto, being the friendly and curious person he is, offers to help her. They then explore the ninja world together, with Mirajane learning about ninjutsu and Naruto learning about Fairy Tail magic.