There are fanfictions where Naruto uses the black fire after making a pact with a powerful entity. This entity could have granted him the ability to use the black fire. He may use it in a strategic way during battles, like surrounding his opponents with walls of black fire to trap them.
One possibility in this fanfiction is that Naruto is exposed to a powerful and otherworldly energy source. This energy could be from a different dimension or a long - forgotten relic. When he comes into contact with it, his body absorbs and adapts to it in a way that allows him to control black fire. This new power also comes with its own set of challenges and responsibilities for Naruto as he tries to integrate it into his existing set of skills.
In some fanfictions, Naruto might learn to use black lightning through special training with a powerful ninja who has mastered it. Maybe he discovers a new chakra nature within himself that allows him to manifest the black lightning.
In fanfiction, black fire bending can be seen as an exotic and powerful addition to the Naruto universe. It could be a result of some ancient and forgotten jutsu that has been rediscovered. For example, a hidden scroll might hold the secrets to black fire bending, and a curious ninja stumbles upon it. This new power then sets them apart from other ninjas, as black fire is often depicted as more dangerous and harder to control than regular fire in fanfiction.
In some fanfics, Naruto might learn to use Black Lightning through special training with a master who has knowledge of this unique ability. Maybe he discovers an ancient scroll or meets a hidden shinobi who teaches him the secrets behind it.
In some fanfictions, Naruto might use chakra strings in a similar way to how Sasuke uses his chakra to control his sword. He could send out his chakra in the form of strings to manipulate objects from a distance. For example, he could use them to pull weapons out of an enemy's hand or to tie up an opponent.
In some fanfictions, Naruto might use Susanoo through some sort of power - sharing or fusion. For example, if there is a plot device that allows him to access the power of the Uchiha, he could potentially use Susanoo. Maybe a powerful enemy forces him to find new ways to power up and he somehow taps into this ability.
In some fanfictions, Naruto might be depicted using the Black Leg Style. This could be a creative way for the author to blend different elements from various anime. Usually, it would involve Naruto incorporating the powerful kicking techniques characteristic of the Black Leg Style into his combat repertoire. However, this is not part of the original Naruto canon, but fanfiction allows for such interesting crossovers.
He could use it for offense, like shooting out intense streams of fire at his enemies. It would be a more direct and powerful form of fire - based attack compared to some of his regular jutsu.
Well, in certain fanfiction scenarios, Naruto discovers his ability to use Yin Release. He may use it in combination with his shadow clones. For example, he sends out clones that are imbued with Yin Release energy to infiltrate an enemy's mind or to disrupt their chakra flow on a spiritual level. This gives him an edge in battles as it's an unexpected and unique way of attacking.
Well, in fanfiction, Naruto could use Storm Release if the author decides to give him an experimental power - up. It could be related to his Nine - Tails chakra mixing with some special elemental energy in the fan - created story. For example, during a battle against a powerful enemy, the Nine - Tails' chakra reacts with an ancient storm - based energy source and Naruto suddenly gains the ability to use Storm Release.