In this fanfiction, the antagonist could also be an internal struggle within Naruto himself. His new god - like powers might come with a price, like a struggle between his human emotions and his new divine nature. Additionally, there could be jealous ninja within his own village who, despite his new status, still try to undermine him. They might spread false rumors or try to sabotage his attempts to bring positive change, all because they are envious of his new - found powers and status.
There could be other ninja villages that see Naruto's new powers as a threat. They might form alliances to oppose him, fearing that he will use his god - like abilities to dominate them. Also, there might be dark forces or ancient evils that awaken because of Naruto's transformation. These entities could oppose him as they try to maintain the balance of power in their own dark ways.
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.
One possible antagonist could be Orochimaru. He might be interested in Naruto's new Shadowman powers and try to steal them for his own evil purposes.
It could be the very people who banished Naruto in the first place. They might fear his new - found power and try to stop him from returning to the village or from getting revenge. They would likely use underhanded tactics to try and take him down.
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.
In this kind of fanfiction, Naruto might gain extraordinary powers that are god - like. He could use his newfound powers to reshape the ninja world in ways that were previously unimaginable, perhaps creating a more just and peaceful place.
In a few fanfictions, it could be a jealous ninja within the village. Maybe someone who has feelings for Naruto and sees Sakura as an obstacle. This ninja could create a false narrative that leads to Sakura's banishment, thus becoming the main antagonist in the story.
A plot twist might be that Naruto discovers that being a monk is actually a key to unlocking a hidden power within him that has nothing to do with chakra. This new power could be related to his spiritual enlightenment and could change the balance of power in the Naruto universe in the fanfiction. Another twist could be that his friends, believing he has abandoned them, turn against him at first, but then later realize that his new path is actually for a greater good and they end up joining him in some way.
One possible antagonist could be Kronos. Since Percy is becoming a Titan of Time, Kronos, who has his own history with time - related power plays, might see Percy as a threat and try to stop him. Another could be the gods themselves. They might not want a demigod to have such a powerful Titan - like status related to time.