One common theme is the power combination. Since Naruto has his ninja powers and Fairy Tail characters have magic, seeing how these powers interact and combine in the harem scenario is often explored. For example, Naruto might use his shadow clone jutsu in a new way with the help of Fairy Tail magic.
One common trope is the power - up. The main character, often from Naruto's world, might gain new and unique powers from the Fairy Tail universe. For example, they could learn Fairy Tail magic on top of their ninja skills. Another trope is the relationship building. In a harem setting, the main character forms deep bonds with multiple characters from both series. There's usually a lot of comical misunderstandings among the characters in the harem as well, like when a character misinterprets a friendly gesture as a romantic one.
Erza from Fairy Tail could also be a main character in this type of fanfiction. She is strong, independent, and has a complex personality. In a Naruto x Fairy Tail crossover, she could form a harem of her own, with Naruto characters being attracted to her strength and Fairy Tail characters having their own relationships with her. Her leadership skills and magical abilities would play an important role in any story that unfolds.
Yes, there are likely some out there. You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for the relevant tags like 'Naruto', 'Fairy Tail', and 'harem' to find such fanfictions.
One great 'Fairy Tail Natsu x Harem' fanfiction is 'A New Adventure'. It has an interesting plot where Natsu finds himself in various unexpected situations with the harem members. The character development is well - done, especially how Natsu's relationships with each of the harem characters evolve over time.
There's also 'Naruto in the Fairy Tail World: Harem Adventure'. In this fanfic, Naruto finds himself in the Fairy Tail universe and gradually forms a harem with various Fairy Tail characters. It's full of action and some light - hearted romance. The interactions between Naruto and the Fairy Tail members are well - written and engaging.
One popular pairing is Naruto and Lucy from Fairy Tail. Naruto's determination and Lucy's intelligence and magical abilities make for an interesting combination. Another is Sasuke and Erza. Their strong - willed and somewhat aloof personalities can create a lot of tension and potential for character development in the fanfic. And then there's Kakashi and Mirajane. Kakashi's laid - back yet highly skilled nature paired with Mirajane's kind and powerful self can be quite appealing.
Perhaps a plot where a powerful villain threatens both the Naruto and Fairy Tail universes. The characters then combine their skills, like Naruto's ninjutsu and Fairy Tail's magic. In the harem part, it could be that the main character, say a new character created for this fanfiction, has to navigate the different personalities and affections of characters from both series while they all work towards saving their worlds.
One common theme is the power - up. Naruto, already a powerful character in his own series, often gains new powers or enhances his existing ones in the Fairy Tail world, which attracts the female characters. Another theme is the sense of adventure. They embark on quests together, which brings them closer and forms the basis of the harem relationships.
One popular Naruto and Fairy Tail harem fanfiction is 'Naruto in the World of Fairy Tail'. It combines the unique powers and characters from both series in an interesting way. The story often has Naruto interacting with the Fairy Tail guild members and developing relationships with some of the female characters from both universes.