Who could be the main villain in a 'fire fist naruto fanfiction'?

Rock Lee could be a great main character. He's known for his taijutsu skills, and adding the Explosive Fist to his repertoire would make for an exciting story. He could use it to overcome his limitations in ninjutsu and genjutsu and prove himself even more as a powerful ninja.

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.

It could be Orochimaru. He's always interested in new forms of power and experimentation. He might see Wolverine as an interesting specimen to study and try to extract his healing factor or adamantium for his own purposes. This would put him in direct conflict with both Wolverine and Naruto, who would naturally oppose Orochimaru's evil plans.

Danzo could be a great main villain in a Naruto Frankenstein fanfiction. He's always been power - hungry and secretive. He might use the concept of creating a Frankenstein - like being to gain more power for Konoha in his own twisted way, but really it's all about his own control. He could be using parts of dead ninja's abilities or something like that, and Naruto would have to stop him.

Orochimaru could be a likely main villain. He has always been interested in Naruto's power and body. Maybe he finally devises a plan to kidnap Naruto and use his body for his own reincarnation experiments.

It could be Orochimaru. He might be interested in stealing the exosuit to enhance his own powers and immortality research. He could see the exosuit as a new way to achieve physical enhancements beyond what his current jutsu can do.

Another possibility is that the main villain could be a spirit or entity that has been trapped for centuries. It uses its influence to make the Hidden Leaf Village conduct 'experiment 101' on Naruto. The spirit hopes to use Naruto's body as a vessel to be reborn into the world and wreak havoc. So it manipulates the events and people involved in the experiment from the shadows.

Maybe Tsunade. She is known for her love of sake. She could have some hidden knowledge of the Drunken Fist. Since she is also a very powerful ninja, she could train Naruto in both the physical and strategic aspects of the Drunken Fist. She could show him how to use his chakra more effectively while performing the drunken - like maneuvers.

There's a possibility that it's a spirit or a ghost of a past master of the drunken fist. Naruto somehow makes contact with this entity, and the spirit decides to pass on its knowledge to Naruto, guiding him through the process of mastering the drunken fist in a rather supernatural way.

It could be a powerful dark wizard who has infiltrated the Ministry of Magic and manipulated the Goblet of Fire. They might want Harry out of the way to further their own dark plans.