A fanfic could focus on a new character who has the powers of Naruto's chakra system and is also related to the Strauss family in the Fairy Tail world. This character could go on adventures in both the Naruto and Fairy Tail universes, facing challenges like the Akatsuki in Naruto and dark guilds in Fairy Tail. They might use Naruto - style combat techniques along with Fairy Tail magic.
One idea could be a character from Fairy Tail who somehow gains the ability to use Naruto's Wood Style. For example, Natsu could discover a magical item during one of his adventures that gives him this power. He might initially struggle to control it as it's a completely different type of magic/ability compared to his Fire Dragon Slayer magic. But as he practices, he could start using it in unique ways, like creating wooden constructs to fight enemies or using the wood to trap opponents in a forest - like environment.
First, do research on all three elements. Know the characters, powers, and settings of Naruto, Strauss (presumably from Fairy Tail), and Fairy Tail itself. Then, come up with an interesting plot that combines these elements in a unique way. For example, a conflict that can only be resolved by using both Naruto's ninjutsu and Fairy Tail magic. Also, make sure to write engaging dialogues for the characters.
Another concept could be that characters from Fairy Tail visit the Naruto world. Natsu, for example, might be intrigued by Gaara's control over sand, which is somewhat similar to his own fire - based magic in terms of its unique nature. And they could all participate in the Chunin Exams together, which would be a chaotic and exciting event.
One idea could be that Baby Naruto somehow gets transported to the Fairy Tail world. He could end up being taken in by one of the guild members, like Lucy. Since he's a baby, he'd be super cute and the members would be protective of him. They might even try to train him in their magic, which could lead to some really interesting and funny situations as Naruto tries to adapt to this new world of magic.
A crossover where a Fairy Tail mage ends up in the Naruto world with amnesia. The ninja initially suspect the mage is an enemy, but as they start to understand the mage's situation, they try to help. In the process, the mage discovers new types of magic by interacting with the chakra - based techniques in Naruto, and this new knowledge could potentially change the way magic works in their own Fairy Tail world once they return.
Another fanfiction concept could be that Erza somehow ends up in the Naruto universe. She might join Naruto's team for a mission. Erza's strong sense of justice and her powerful magic would be really interesting to see in the context of Naruto's world. For example, she could use her armor magic to help Naruto and his friends in a battle against a powerful enemy.
Perhaps a fanfiction where a chaos mage from another dimension is sent to both the Naruto and Fairy Tail universes to steal powerful artifacts. This would force the heroes from both worlds to team up. The Naruto characters could contribute their unique jutsu, while the Fairy Tail wizards use their magic, all while trying to figure out the chaos mage's motives and powers.
A lot of these crossovers explore the friendships that could form between characters from the two universes. Picture Natsu from Fairy Tail and Naruto becoming friends. They both have a strong sense of justice and loyalty, so it's fun to read about them teaming up against common enemies. You can find these fanfictions on various fanfic websites.
One idea could be that Venom somehow ends up in the Naruto universe. Maybe a strange rift in dimensions brings Venom to Konoha. He could initially be seen as a threat, but Naruto, with his ability to see the good in people (or in this case, symbiotes), tries to befriend Venom. This could lead to some really interesting battles and storylines, like Venom helping Naruto against powerful enemies using his unique powers.
A fanfic could be written where Alita is reincarnated in the Naruto universe as a ninja. She retains her combat skills but has to learn how to use chakra. Naruto becomes her friend and helps her adapt. They go on adventures together, facing off against powerful enemies. Alita's unique fighting style would make her stand out among the ninjas, and together they could become a formidable team.