In this fanfiction, it's possible that the main antagonists are some power - hungry individuals in Iwa who fear Naruto's influence. They may be worried that Naruto will gain too much popularity among the villagers and the younger generation of ninjas. Another possible antagonist could be an old enemy of Iwa who sees Naruto's arrival as an opportunity to strike at the village. They might think that with Naruto being a new and potentially unstable element in Iwa, they can cause chaos and destruction more easily.
The main antagonists could be some of the conservative Iwa ninjas who oppose Naruto joining their village. They might see him as a threat to their traditional ways and values. Also, there could be some rogue ninjas from other villages who target Naruto because they see him as an easy target now that he's in a new and unfamiliar environment.
Maybe there's a corrupt elder in Iwa who doesn't trust outsiders. This elder sees Naruto as a threat to Iwa's traditional ways and tries to get rid of him. He might spread false rumors about Naruto within the village and try to turn the other ninjas against him.
It could be the ninja from Naruto's former village who don't want him to succeed in his new place. They might see his new - found influence as a threat and try to undermine him.
One possible plot development could be Naruto facing initial hostility in Iwa. Since he's from Konoha, the Iwa ninjas might be suspicious of him at first. But Naruto, with his determination and unique skills like the Rasengan, could gradually earn their respect. He might also learn new jutsu unique to Iwa and form new alliances, perhaps even finding a way to bridge the gap between Konoha and Iwa in the long run.
Well, one possibility could be that Naruto is banished from Konoha due to some false accusations. When he joins Iwa, he might start learning their unique jutsu and fighting styles. He could also face a lot of distrust at first from the Iwa ninjas because he's from Konoha. But as time passes, he proves himself and becomes an important part of Iwa, maybe even leading some missions against common enemies of both villages.
The main antagonists could be the ones who banished Naruto in the first place. Maybe it was a group of elders in the village who feared Naruto's power and wanted to get rid of him. They would see Naruto as a threat now that he is becoming the Onikage and would try to stop him from returning to the village or causing any changes.
The main antagonists could be some of the conservative elders in the Hidden Leaf Village. They banished Naruto in the first place and would see his rebuilding of the Uzumaki clan as a threat to their power. They might try to undermine his efforts by spreading false rumors about him and his new clan.
The village elders could be the main antagonists. They might see Naruto's godlike powers as a threat to their traditional way of ruling the village and decide to get rid of him. Another option could be a secret organization within the village that wants to use Naruto's power for their own evil purposes and when he refuses, they turn on him.
It could be Orochimaru. He's always been interested in power and the hunt for powerful things. He might see fem Naruto as a threat or a potential source of power. He could try to capture her or stop her from achieving her goals in the hunt.
Often, the main antagonists can be the village elders or some corrupt shinobi within the village who are behind their banishment. These characters may fear Naruto and Naruko's growing power and influence.
There could be an outside force, like a neighboring village that wants to keep Naruto and Sasuke away from their own village. They might be afraid of the potential power and influence Naruto and Sasuke could bring back if they return. So, this neighboring village sends their best ninjas to hunt down Naruto and Sasuke during their banishment, making them the main antagonists in the fanfiction.