The main antagonists could be those who were once enemies of Obito. They might see Naruto as a threat simply because of his relation to Obito. For example, some of the old - school ninja clans who still hold grudges against Obito's actions in the past could target Naruto.
Well, it could be about Naruto facing unique challenges because of his relation to Obito. Maybe he discovers some hidden powers passed down from Obito. He might also struggle with the reputation that comes with being related to someone who had a complex past like Obito.
It could be those who fear Naruto's power as the son of Lilith. For example, some of the more traditional ninja clans might see him as a threat to their power and status in the ninja world.
Maybe there could be an Asgardian traitor who doesn't like the idea of a half - human being part of the royal family. This traitor could team up with some of Naruto's enemies from the ninja world to create chaos. They could plot to steal Naruto's powers or his special weapon if he has one, and Naruto has to stop them to protect both Asgard and the ninja world.
It could be the people in the village who are against Naruto because of his new identity as the son of Manda. They might see him as a threat to the village's stability.
The main antagonists could be the Akatsuki from the Naruto world. They might see Naruto's new powers as a result of being Sparda's son as a great asset and try to capture him to use for their own evil plans, like creating some sort of super - weapon or using his power to take over the ninja world.
Well, perhaps there could be a powerful underwater clan that sees Naruto as an abomination because he is a half - human, half - Neptune's son. They view his existence as a threat to the balance of the ocean realm and the ninja world. They send their best warriors to stop Naruto from growing in power and spreading his influence. Also, a mad scientist - type character who wants to experiment on Naruto to unlock the secrets of his Neptune - heritage could be an antagonist.
One possible main antagonist could be a rogue ninja who was once an apprentice of Orochimaru and is jealous of Naruto's connection to the Sannin. This ninja might want to steal Naruto's new - found powers related to the Sannin. Another could be a hidden organization that sees Naruto as a threat because of his potential with the Sannin's abilities. They fear he will disrupt their plans for power in the ninja world.
One possible antagonist could be a jealous Roman god who doesn't want Naruto, as the son of Jupiter, to gain too much power. Maybe Pluto, who might see Naruto as a threat to his own domain in the afterlife.
The Akatsuki could still be major antagonists. Their goals of collecting the tailed beasts would put them in direct conflict with Naruto, especially if he has the added power from his relation to Esdeath. They might see him as an even greater threat.
One possible antagonist could be those who oppose the mixing of the Naruto world and the Greek mythology elements. They might see Naruto as an abomination because of his unique heritage as the son of Demeter. Another could be some of the traditional Naruto villains who now see Naruto as an even greater threat due to his newfound powers related to Demeter. For example, Orochimaru might be interested in Naruto's powers for his own evil experiments.