Rock Lee would be a strong contender. He's dedicated his whole life to taijutsu. His ability to open the gates gives him superhuman strength and speed, which would make him a formidable fist fighter.
One idea could be a tournament where Naruto characters use their fist - fighting skills. For example, Naruto could face off against Sasuke in a no - jutsu, just pure fist - fighting battle. It would be intense as they both have their own unique fighting styles. Naruto's more energetic and improvisational style against Sasuke's calculated and precise strikes.
One common theme is the struggle for power. Naruto has to push himself to the limits to become a brutal fighter, often facing stronger opponents. Another theme is self - discovery. As he becomes more brutal in his fighting, he also discovers new aspects of himself.
Well, Naruto is definitely one of the main characters since it's in the title. He would be the central fighter. Sakura might also be a main character, perhaps as Naruto's support or even as a fighter herself, using her medical ninjutsu in combat in new and creative ways.
A great fanfiction concept would be a crossover where Naruto is taught the art of the fire fist by a character from another anime. This could lead to new and exciting battles as he combines his existing skills with the new fire fist power.
I'm not entirely sure as there could be many interpretations. It might be a fan - made story that involves a unique fighting style or technique related to Naruto, perhaps a new form of the 'ninth fist' that the author has created within the Naruto universe.
One possible plot could be Naruto using his ninja skills in the context of flying. Maybe he has to use his quick reflexes to dodge enemy fire while in the air. His ability to sense danger could be translated into anticipating enemy attacks during aerial battles.
Maybe Naruto is transported into the Street Fighter world. He could use his ninja skills in the Street Fighter battles, like using his shadow clones to confuse opponents. And perhaps he teams up with some of the Street Fighter characters to fight against a common enemy.
I'm not sure about a specific 'Naruto is a Street Fighter' fanfiction to recommend. You could try searching on fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a wide variety of fan - made stories.