There are many great ones. For Naruto fanfiction, 'A New Path' is quite interesting as it explores an alternate future for Naruto. Regarding Sparda, since he is from Devil May Cry, a fanfic like 'Sparda's Legacy' delves into his past and how it impacts the present. In Fairy Tail fanfiction, 'The Lost Mages' is popular as it focuses on a group of mages who were forgotten but have a crucial role to play.
First, do your research. For Naruto, know the different ninja clans, jutsus, and the overall world - building. For Sparda, understand his backstory and the Devil May Cry universe's lore. In Fairy Tail, be familiar with the magic types and the guild's dynamics. Then, come up with an interesting concept that combines elements from all three. For example, a story where Naruto visits the world of Fairy Tail and meets a character related to Sparda.
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.
Well, if Naruto was in the S - Class of Fairy Tail, his combat skills would be a great addition. Naruto's ability to use shadow clones could be used for various strategic purposes during Fairy Tail's missions. He could send clones to scout ahead or create distractions in battles against dark guilds.
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.
Sure, they can. Fairy Tail is used to dealing with all sorts of magical and extraordinary things. Naruto fanfiction, despite being from a different universe, would still have elements that they could relate to. The themes of friendship, courage, and fighting for what's right are common in both Fairy Tail and Naruto. So, while there would be some unfamiliar terms and concepts, overall, they would be able to make sense of the fanfiction.