Madara Uchiha can also be a common antagonist in Naruto suffering fanfictions. He might be resurrected in a more powerful and malevolent form. His plans could involve directly causing harm to Naruto, either physically or by manipulating the people around him. Also, there could be new, original antagonists created by the fanfiction authors. These could be powerful dark mages or shadowy organizations that target Naruto specifically to further their own evil agendas.
Often, Orochimaru can be a typical antagonist. Given his interest in immortality and dark jutsu, he might see Naruto's new state as a threat or something to be exploited. Another could be new, original characters created specifically for the fanfiction. These might be dark immortals themselves who oppose Naruto for various reasons, like territorial disputes or power struggles.
Typical antagonists in this kind of fanfiction can be various. The Sith, as we know, are always a likely candidate. They seek power and might see a kidnapped Jedi as a means to an end, like getting access to ancient Jedi secrets. But it's not just them. There could be rogue elements within the galaxy who oppose the Jedi for different reasons. Some might be power - hungry warlords who think a kidnapped Jedi can give them an edge in their territorial disputes. Also, there are the shadowy criminal organizations that might kidnap a Jedi for ransom or to sell on the black market. They don't care about the Jedi - Sith conflict; they just see an opportunity for profit or power.
In these novels, the antagonists can vary. One group could be the jealous gods. They are envious of the protagonist's special abilities or unique reincarnation as a god, so they try to undermine them. Another type of antagonist could be the ancient evils that have been sealed away for a long time. The new god's presence might accidentally release or anger these evils, leading to conflict. Mortal organizations with extreme beliefs that oppose the new god's ideology can also be antagonists.
Orochimaru is often a common antagonist in these types of fanfictions. He has a history of experimenting on people and his knowledge of jutsu could be used to brainwash Naruto. He might want to use Naruto's power for his own evil plans.
The Akatsuki could be likely antagonists. They are always interested in powerful ninja like Naruto. They might use some forbidden jutsu to control Naruto to further their goals of collecting the tailed beasts. Another possibility is Orochimaru. He is always looking for ways to gain power and Naruto's power would be very appealing. He could try to control Naruto to use him in his experiments or to fight his enemies for him.
The Akatsuki could be a likely antagonist. Since they were always a threat in the original series, in a Konoha - destroyed scenario, they might try to capitalize on the chaos and further their own goals.
Sasuke can often be an antagonist in these types of fanfictions. Since Sasuke is also power - hungry in the original series, he and Naruto's quests for power could put them at odds. Their rivalry could be intensified as Naruto becomes more and more obsessed with power, leading to some epic battles between them.
Often, ancient and powerful demons or dark gods can be antagonists. They might see Naruto's newfound godhood as a threat to their own power or plans. For example, a demon that has been sealed away for centuries could be awakened by Naruto's ascension and seek to destroy him.
Well, the main antagonists could be a group of rogue ninja who are hired by a powerful nation to take down Naruto. Since he is unkillable, they would have to use more underhanded tactics like trying to isolate him from his friends and allies. Or perhaps there is a dark force that is awakened by Naruto's unkillable state, thinking that he is a threat to the balance of the ninja world. This dark force could then become the main antagonist, trying to destroy Naruto at all costs.
One potential antagonist could be a rogue ninja who also has aerokinesis but uses it for evil. He might be jealous of Naruto's natural talent and try to undermine him at every turn. Another could be a powerful sorcerer from a far - off land who has come to the Naruto universe specifically to find someone with aerokinesis to either steal their power or use them as a tool. There could also be a group of anti - ninja who see Naruto's new power as a threat to their plans of overthrowing the ninja system and they try to eliminate him.