Who could be the main antagonist in a 'Naruto Demon of the Hidden Leaf Fanfiction'?

It could be a rogue ninja from the Hidden Leaf's past who has come back for revenge. Maybe someone who was wronged by the village long ago and has now amassed great power to destroy it. Another possibility is a new enemy from outside the village, like a powerful warlord from a far - off land who wants to conquer the Hidden Leaf for its resources.

It could be an old enemy who has resurfaced and found a way to turn Naruto against the Leaf. Maybe Orochimaru, who has always been interested in Naruto's power, manipulates him into attacking the village. Orochimaru could use his knowledge of dark jutsu to influence Naruto's mind.

It could be Orochimaru. He is always interested in new and powerful weapons. With Naruto having hidden blades, Orochimaru might see it as a threat and try to take the blades for himself, leading to a conflict.

It could be a rogue ninja who was once part of the same clan that the hidden blade belongs to. He wants the blade back to gain ultimate power and is willing to do anything to get it from Naruto.

It could be a rogue ninja who has made a pact with the demons in the demon world. This ninja has turned against the ninja world and wants to use the power of the demon world to rule over all. He would constantly oppose Naruto's attempts to restore peace.

It could be an ancient demon lord who wants to enslave both the demon prince and Naruto. This demon lord might see the unique bond between them as a threat to his plans of domination.

Obviously, the demon overlord could be the main antagonist. He might have his own motives like ruling the ninja world or obtaining some powerful jutsu that Naruto and his friends are trying to protect.

Since it's a fanfiction, it could have Naruto as one of the main characters. And depending on the plot, there might be a new character who is the demon. Maybe Sasuke could also be involved if the story ties into the existing Naruto - Sasuke dynamic in some way.

It could be a rogue ninja from a forgotten clan who is jealous of Naruto's new - found power from his hidden bloodline. This antagonist might try to steal Naruto's bloodline ability for himself.

It could be a new and powerful trainer who has a vendetta against Ash. This trainer might see Ash as a threat to their own rise to the top in the Pokemon world. They could manipulate Leaf into betraying Ash to further their own goals.