The ANBU black ops in Konoha could also be antagonists. If Naruto is against Konoha, they would be the ones sent to stop him. They are highly skilled and loyal to Konoha. Their actions to stop Naruto could be seen as them standing in the way of Naruto's revenge. They might use underhanded tactics, which would only fuel Naruto's desire for revenge even more.
The elders of Konoha could be the main antagonists. They are often the ones making the big decisions in the village. If Naruto is seeking revenge, it could be because of their actions, like how they treated him when he was a child or how they might have hidden important information from him.
A 'naruto takes revenge on konoha fanfic' might involve Naruto feeling betrayed by Konoha. Maybe he was wrongly accused of a crime he didn't commit. As a result, he teams up with some of his old enemies who also have grudges against Konoha. Together, they plan a large - scale attack on Konoha. Naruto, with his newfound power and allies, aims to topple the current regime in Konoha and establish a new order where justice is truly served.
Maybe the hidden organizations within Konoha that work in the shadows. They could have been involved in some plot against Naruto that led to his decision for revenge. They would be the ones trying to stop Naruto from exposing their secrets and exacting his revenge on the village as a whole.
The ANBU black ops could also play the role of antagonists. They are the ones who carry out the village's more secretive and sometimes morally gray missions. If they are ordered to hunt Naruto down unjustly, they would be in Naruto's way and could be the reason for his violent reaction towards Konoha.
The hidden enemies within Konoha who oppose Naruto's ideas of peace and unity could be antagonists. They might spread false rumors about Naruto, turning the villagers against him. This growing animosity between Naruto and the village could result in him lashing out at Konoha, making those who spread the rumors antagonists in the fanfic.
The elders of Konoha could be the main antagonists. They are often shown to be power - hungry and willing to do whatever it takes to maintain their control over the village. They might see Naruto as a threat to their authority and decide to betray him. Another possibility is Danzo. He has always had his own agenda and has been shown to be ruthless in achieving his goals. He could easily be the one behind the betrayal of Naruto in a fanfic.
Maybe Danzo could be a major antagonist. He's always been a shadowy figure with his own agendas. He might see Naruto as a threat to his secret operations and influence in Konoha, and thus play a key role in getting Naruto executed.
The Akatsuki could also be antagonists. Since Madara has his own plans with Naruto, the Akatsuki might see this as a disruption to their goals, especially if Naruto is being groomed by Madara to oppose them. They would try to stop Madara from influencing Naruto further.
Obviously, Naruto would be the main character as it's about his revenge on Konoha. Sasuke could also play a significant role. He has his own issues with the village, and he might either support Naruto's revenge or try to stop him depending on how his character is developed in the fanfic. Sakura might be there too. She could be caught in the middle, trying to figure out whether to side with Naruto or stay loyal to Konoha. And Kakashi, as Naruto's former teacher, would likely be involved. He might be one of the people Naruto has to face if he's set on his revenge, or he could be trying to reason with Naruto.
Madara Uchiha could also be a possible antagonist in this scenario. Even if he is dead in the original story, in a fanfiction, his lingering influence or a resurrected form could manipulate Naruto. Madara was always against Konoha's ideals to some extent and might use Naruto as a tool to destroy what he hated.
The traditionalist elders might oppose Naruto. They are used to the old ways of running Konoha and may see Naruto's takeover as a threat to their power and influence.