It could potentially mean that in a fan - created fictional work, Naruto's story is somehow related to the end of Fairy Tail. Maybe it's a crossover fanfic where events in Naruto lead to the conclusion of Fairy Tail's story in that particular fic.
No, it's not a common concept. Naruto and Fairy Tail are two distinct anime/manga series. While there are crossover fanfictions between them, the idea of Naruto being directly related to the 'end' of Fairy Tail fanfiction is rather unusual and not something you'd typically see.
To end a Fairy Tail fanfiction, it could be interesting to look at the future. After the main events of the story are over, write a short epilogue that shows where the characters are headed. Are they going on new adventures? Have they retired from the guild? You can also end it on a bittersweet note. For instance, a character may have to leave the guild to pursue a personal dream, but they leave with the love and support of their friends, showing that change can be both sad and positive.
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.
One popular 'End Join Fairy Tail' fanfiction might be 'The New Adventure'. It often features new characters joining the Fairy Tail guild and going on unique quests. Another could be 'End Join: The Power Within' which focuses on the development of the joined characters' powers within the Fairy Tail universe.
Sure, in the 'Fairy Tail' universe, the concept of Natsu being END is quite fascinating. Fanfiction writers often take this idea and run with it. They might create stories where Natsu discovers his true nature as END more gradually, or they could write about how the other guild members react when they find out. It can also lead to stories that explore the origin of Natsu as END and how it ties into the overall lore of the 'Fairy Tail' world.
First, you need to know the Fairy Tail universe well. Read the original manga or watch the anime. Then, think about the characters you want to have join at the end. Create a backstory for them that fits into the Fairy Tail world. For example, if it's a character from a different land, explain how they heard about Fairy Tail and what made them want to join.
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.