A secret organization within Konoha that has its own agenda. They want to take over the village gradually and see Naruto and Kakashi as obstacles. So they engineer their banishment to further their own plans.
The village elders could be antagonists. They might see Naruto and Kakashi as threats to their traditional way of ruling the village and use false accusations to banish them.
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.
Danzo might be an antagonist. He's always been power - hungry and might see Naruto as a threat, especially if Kakashi is guiding and protecting him. Danzo could try to undermine Kakashi's efforts to raise Naruto and might even send his root agents to spy on them or cause trouble.
Well, it could be Orochimaru. He was always up to no good and had an interest in powerful ninja. He might target Naruto and Temari to either steal their powers or use them for his evil experiments, which would surely lead to them getting hurt.
One possible antagonist could be a rogue ninja from another village. They might target Tenten for her unique weapon - handling skills, thinking they can use her to create powerful weapons for themselves. Naruto would then have to face this ninja to save Tenten.
Perhaps some rogue ninja from other villages. They might see Naruto as a symbol of Konoha's power and want to take him down to weaken Konoha. These rogue ninjas could be led by a powerful and vengeful shinobi who has a grudge against Konoha. So when Naruto is alone on a mission or something, they attack, and that's when Minato steps in to save him.
It could be some rogue ninja clans that are after Karin for her special abilities. They might see her as a tool to gain power or information. For instance, a clan that specializes in blood - related jutsu might want to use Karin's unique blood - sensing ability for their own evil purposes.
The Hidden Leaf Village itself could be an antagonist. If Naruto goes evil, the village that once was his home would be against him now.
One likely antagonist could be those who fear Naruto's new power. For example, some of the traditional shinobi clans who are used to being in power might see Naruto as a threat. Another could be ancient evil forces that were sealed away long ago and now sense Naruto's god - like power as a way to break free. They might try to either corrupt Naruto or destroy him to prevent him from stopping their plans.
One potential antagonist could be a power - hungry shinobi from another village. They might view Hayate as a threat to their plans, maybe because Hayate is involved in some sort of peace - keeping mission between villages. So, they try to eliminate him. And Naruto, being the defender of his comrades, will not stand by and let that happen. There could also be a group of missing - ninjas who band together to take on Hayate, thinking he's an easy prey, but they underestimate Naruto's loyalty and strength.