It could be some powerful local warlords who are exploiting the resources of the Land of Wave. They might have their own private armies of ninjas and use fear to keep the people in check.
There might be a corrupt noble family within the Land of Wave. They have been in power for a long time and are only interested in maintaining their luxurious lifestyles. They oppose any change that Naruto tries to bring and will do anything to stop him from liberating the land.
In this fanfiction, Naruto might use his unique jutsus like the Rasengan. He could start by uniting the villagers in the Land of Wave who are oppressed. He'd probably face off against the corrupt leaders or powerful enemies controlling the land. His determination and never - give - up attitude would inspire the locals to fight for their freedom.
One possible main antagonist could be a rogue ninja from a forgotten clan who has a vendetta against the Land of Fire. They might be seeking revenge for something that happened in the past and see Naruto as the symbol of the new regime they want to topple.
The Sound Ninjas could be great antagonists. They could use their own unique parkour - like skills to try and stop Naruto. They might be chasing him through the forest, and Naruto has to use his parkour skills to outmaneuver them.
Maybe some corrupt officials within the prison system itself. They oppose Naruto's more humane and reform - focused approach to prison management. They might try to undermine him at every turn, for example, by cutting off resources or spreading false rumors about him among the prisoners.
Maybe a group of dark - type Pokémon that have banded together and are trying to overthrow Arceus. They view Naruto as an easy target at first, but quickly realize he is a formidable opponent with his ninja skills and new Pokémon - related powers. They would constantly try to undermine Naruto and his efforts to protect the Pokémon world.
It might be a rogue ninja from the Wave. They could have a vendetta against Konoha and see Naruto as an easy target to frame and cause chaos between the two places.
The Hidden Leaf Village elders could be main antagonists. If Naruto turns dark because he feels betrayed by the village, they would be the ones representing the establishment he is against. Their conservative and sometimes self - serving ways could be the catalyst for Naruto's transformation, and then they would be the ones trying to stop him as he becomes a threat to their power and the village's traditional order.
It could be the traditional enemies from Naruto's world, like the Akatsuki. They might see the union of Naruto and Rias and their unborn child as a threat to their plans for world domination. They could try to kidnap Rias to use her as a bargaining chip against Naruto or to study the unique nature of their child.
The village elders could be antagonists. They might see Naruto as a threat due to his devil - like origin and try to eliminate him. They fear that his powers could bring chaos to the village.
One likely main antagonist could be a powerful demon lord who is trying to break through the barriers between the spirit world and the human world. This demon lord would be a major threat to Naruto and his harem, and they would have to use all their combined skills to stop it.