His chakra. Chakra is like the energy source in Naruto's world. In the fanfiction, this chakra could be translated into a very powerful form of magic in Fairy Tail. It gives him the ability to perform various powerful techniques, much like mages in Fairy Tail use their magic.
One storyline could be that the British mage is accidentally transported to the Naruto world. They then have to find a way to get back home while also dealing with the various threats in the Naruto universe. Along the way, they could make friends with Naruto and his friends and use their magic to help in battles against the Akatsuki.
A British mage might struggle to fit in at first. In the Naruto world, power is mainly based on chakra. But the mage could start by using their magic secretly. For example, they could use magic to heal wounds in a way that's different from medical ninjutsu. Eventually, they might teach some of their magic to Naruto characters or learn from them about chakra. It could be a two - way exchange of knowledge and skills that would change the Naruto universe in unique ways.
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 unique feature is the blend of magic and ninjutsu. For example, in some fanfictions, characters can cast spells like mages while still using their ninja tools. It's like a new power - up for the Naruto characters.
One common theme is the fusion of two different power systems. Naruto's traditional ninja skills are combined with the unique abilities of a gun mage. Another theme could be about Naruto's journey to master this new and strange power. Also, there might be themes of facing new and unexpected enemies that require the use of these combined powers.
One common theme could be power. The black mage usually has some unique powers, and in the Naruto universe, power dynamics are always interesting. Another theme might be identity. The black mage character may struggle with their identity in a world that is not their own, like in Naruto.
Power and its consequences. Since black mages often have great and sometimes dangerous powers, many fanfictions explore how this power affects the character and the Naruto world around them.
One possible plot could be Naruto discovers his mage powers when he tries to save his village from a new and powerful dark magic threat. He has to learn how to control his mage abilities quickly, which are different from his ninja skills. Maybe he teams up with some of his friends who also have latent mage abilities.
In this fanfiction, Kakashi could also be Naruto's mentor in magecraft. Kakashi is known for his adaptability. He could start to study mage powers along with Naruto. They could learn together about new forms of magic, and Kakashi could use his combat experience to help Naruto understand how to use his mage powers in battle situations.