One reason could be the author's intention to explore a different narrative. Maybe they want to show how Naruto would struggle without his usual powers or support system. For example, if he lost his chakra control, it would make him seem weak.
The contrast. When a fanfic features a weak character in the Naruto DxD universe, it creates an interesting dynamic. For example, seeing a character with less power try to survive in a world full of powerful ninjas and devils makes for an exciting read as they have to rely on their wits more than their strength.
One good weak Naruto in Fairy Tail fanfic could be 'Naruto's New Adventure in Fairy Tail'. In this fic, Naruto starts off as a rather weak character in the Fairy Tail world, having to relearn how to use his skills. It has some interesting character interactions, like when he meets Natsu and they have a friendly spar that shows Naruto's initial struggle.
It's very likely that there is. Fanfiction writers love to play with different concepts and universes. In a 'naruto weak fairy tail fanfiction', perhaps the writer is trying to show how Naruto would adapt in a world where he doesn't have his usual strength. He could form new alliances, learn Fairy Tail magic, and develop in ways that are different from his original character arc. But to actually find such fanfiction, it's best to search through popular fanfiction repositories and use the exact phrase 'naruto weak fairy tail fanfiction' in the search bar.
The fanfiction changes the perception by challenging the idea of his invincibility. It forces the readers to consider what Naruto would be like if he wasn't always able to pull through with his signature moves. It might make some readers see him as a more complex character rather than just a one - dimensional hero.
One popular 'naruto pretended to be weak' fanfic is 'The Hidden Strength'. In this fanfic, Naruto disguises his true power for various strategic reasons. Another is 'Weak Facade', where he fools his enemies by acting weak, which leads to some really interesting plot twists.
Well, in fanfiction, anything can happen. But Naruto being a weak Fairy Tail mage seems a bit off. Naruto is a powerful ninja with a strong will. In Fairy Tail, mages also rely on their willpower to some extent. Naruto could potentially draw on his ninja skills and combine them with magic in unique ways. For example, his shadow clone jutsu could be adapted into some form of magical clone spell. His Rasengan could be transformed into a magic - based attack. So, he may face some initial challenges in understanding magic, but he's not likely to be weak.
There are so many fanfics out there that it's hard to specifically name a 'naruto dxd weak fanfic'. However, when you search for fanfics, look for ones where the main character has some kind of weakness that they have to overcome. In the Naruto and DxD universes, this could be related to their powers not being fully developed, or having a psychological weakness. Read the summaries and reviews of the fanfics to see if they match what you're looking for.