Well, one way it could work is if there was some sort of multiverse crossover. Maybe in a strange twist of magic, Naruto could be transported to the Fairy Tail universe and end up related to Mavis. It would be really interesting to see Naruto's ninja skills combined with the magic of Fairy Tail. He could teach the Fairy Tail guild some unique combat techniques.
In some fanfictions, he is a mentor - like figure. He teaches Mavis or other young wizards important lessons about magic, life, and the values of Fairy Tail. This could include things like the importance of friendship in magic, which is a central theme in the Fairy Tail series.
In fanfiction, Mavis' brother can be portrayed in various ways. Some might depict him as a protective figure, always looking out for Mavis before her misfortunes. He could be a strong magic user, with unique abilities that are different from Mavis' own. For example, he might have a more combat - oriented magic compared to Mavis' strategic and leadership - related magic.
Naruto could be a protector. Just like he protected Konoha in his own world, he would protect Mavis and the Fairy Tail guild. His combat skills would be a great asset.
Naruto has shown incredible feats of strength, speed, and endurance. He has defeated some of the most powerful villains in his universe. But Mavis is no slouch either. Her Fairy Law is a very powerful spell. If we consider their growth potential, Naruto has the ability to constantly get stronger by unlocking new forms of his power, like Sage Mode and later the forms related to the tailed beasts. Mavis, on the other hand, has a deep knowledge of magic that could potentially allow her to counter any of Naruto's attacks. It really depends on the situation, the location, and how well they know each other's abilities.
One way could be through a crossover of magic and ninjutsu. Maybe Mavis's brother could have a unique power that is similar to a ninja ability in Naruto. For example, if he has some kind of illusion - based magic, it could be related to the genjutsu in Naruto. Writers could create a scenario where he teams up with Naruto characters, sharing his Fairy Tail - like magic and learning from the ninjas at the same time.
He could be a catalyst for change. Maybe his arrival in the Naruto world disrupts the normal balance, forcing the characters to adapt to new ways of thinking. For example, his Fairy Tail - like values of friendship and loyalty could influence the Naruto characters to reevaluate their own relationships.
One possible plot could be that Naruto somehow gets transported to the Fairy Tail world and meets Mavis. Naruto, with his never - give - up attitude, could inspire Mavis in a new way. He might help her deal with some of the darker forces in the Fairy Tail universe using his ninja skills. For example, Naruto could use his shadow clone jutsu to confuse enemies while Mavis uses her Fairy Magic to attack from another angle. They could also exchange stories about their respective worlds and learn from each other's leadership styles, Naruto as a Hokage - in - training and Mavis as the founder of Fairy Tail.
One popular storyline could be a crossover adventure where Naruto and the Fairy Tail characters, especially with Mavis involved, team up to fight a common, powerful enemy. Maybe an ancient evil that threatens both their worlds.
One common theme is friendship. Just like in the original Naruto and Fairy Tail series, fanfics often emphasize the power of friendship. Characters from both universes come together and form strong bonds. Another theme is power - up. Naruto characters might gain new magical powers from Fairy Tail or vice versa. For example, Naruto could learn some Fairy Tail magic to enhance his combat abilities.