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.
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.
One common theme is power enhancement. Writers often explore ways to make the Gentle Fist more powerful. Another is legacy, like how the technique is passed down through generations.
One common theme is the clash of different fighting styles. The ninjutsu of Naruto characters and the martial arts of Street Fighter characters create really cool battle scenes. For example, Sasuke's lightning - based attacks against Chun - Li's lightning - fast kicks.
It could be Hinata. Since she is a master of the Gentle Fist in the Naruto universe, she would be a logical choice to teach Naruto. She has a deep understanding of the technique and also has a close relationship with Naruto, which would make for an interesting dynamic in the fanfiction.
It could be a rogue ninja who was once a student of a great fire - style master but turned evil. He wants to use the power of the 'fire fist' to destroy all the ninja villages and rule over the world.
Well, perhaps in this 'fire fist naruto fanfiction', the 'fire fist' is actually an ancient power sealed away long ago. Naruto discovers it while on a mission in an old, forgotten temple. He then has to deal with the fact that there are dark forces also after this power, and he has to master it quickly to protect his village. It could lead to some really cool battles and new friendships as he teams up with other ninjas to keep the power safe.
Another plot line could be that Naruto discovers a new form of chakra that is related to being a fighter. This new power source could attract the attention of powerful and malicious forces. He then has to fight to protect this new power and also figure out how to master it without it consuming him.