Madara Uchiha might also be a main antagonist. His goals of reshaping the ninja world could be directly opposed to what Naruto is trying to achieve with his newfound 'godlike' powers. Madara would likely see Naruto as a major obstacle in his grand plan for the shinobi world.
Maybe a new character could be introduced as the main antagonist. A powerful and mysterious ninja who is jealous of Naruto's 'godlike' status. This new character could have their own motives for starting and continuing the Third Shinobi War, and Naruto would have to figure out their identity and motives in order to stop them.
Rock Lee could be an interesting main character for a Third Shinobi War fanfiction. Since he doesn't rely on ninjutsu, his unique fighting style could be a great asset during the war. We could see him face off against powerful ninjutsu users from other villages and prove that taijutsu is just as effective. Also, his unwavering determination could inspire his comrades during the dark times of the war.
It could be a rogue ninja who was once part of a minor group during the war but has now risen to power. Maybe they felt overlooked or mistreated during the war and now seek revenge on the major villages.
It could also be a veteran ninja who has already seen a lot in their life but is still drawn into the Third Shinobi War. This character could have a complex backstory, perhaps they lost someone dear in a previous war and are now fighting to prevent the same from happening to others. Their wisdom and experience could be a key factor in the story.
One possible interesting plot could be Naruto having some unique and super - powerful abilities that completely change the course of the Third Shinobi War. For example, he might be able to instantly teleport across the battlefield and surprise the enemy, turning the tides in his side's favor.
Another possibility is a powerful spirit from the Avatar world that has been corrupted by the introduction of Naruto - like powers. This spirit could resent the intrusion of this new power source and seek to destroy anyone associated with it. It might have unique abilities that combine the spiritual magic of the Avatar world with the raw power of Naruto's chakra, making it a formidable foe.
There's also the possibility that a group of rogue ninjas, who have banded together after being ostracized for their interest in the godlike hollow powers, become the antagonists. They might believe that Naruto is misusing or hoarding these powers and decide to take them by force, leading to a series of intense battles between them and Naruto.
Perhaps a dark entity from another dimension. This entity senses Naruto's powerful bloodline and wants to possess him or use his body as a vessel to enter the Naruto's world and wreak havoc. It would have otherworldly powers that Naruto has never faced before, making it a truly formidable antagonist.
It could be a combination of Orochimaru and Lex Luthor. Orochimaru from the Naruto universe is always seeking power and Lex Luthor from the DC universe is a brilliant but evil mastermind. They could team up, with Orochimaru being interested in Superman - like Naruto's unique physiology and Lex Luthor wanting to use Naruto's power to take over both the Naruto world and the DC world. They would be a formidable duo, constantly devising plans to undermine Naruto and his friends.
There could be some original characters as main characters too. For instance, a young shinobi from a small, unknown village who rises to prominence during the Third Shinobi War. This character could bring a fresh perspective and unique abilities to the story, interacting with the well - known Naruto characters and changing the course of the war in the fanfic.
It could be a powerful ninja from an ancient clan who sees the character with the godlike multi - bloodline as a threat to their own clan's supremacy. This antagonist would be very skilled in traditional ninja arts and would use their knowledge of the old ways to try and defeat the protagonist.