Who would be the main antagonist in a Naruto Poseidon fanfiction?

It could be someone who wants to disrupt the relationship between Naruto and Beerus. Maybe a powerful dark ninja who sees Naruto's newfound connection with Beerus as a threat to his own plans for power.

It could be a rogue ninja from another village who has a vendetta against Konoha. This ninja might target Team 10 specifically because of Naruto's presence, seeing it as an opportunity to make a name for themselves by taking on a powerful shinobi like Naruto.

The Covenant could still be the main antagonists. They are a powerful and menacing force in the Halo universe, and Naruto would have to face their might. Their advanced weaponry and large numbers would pose a great challenge to Naruto.

Another possibility is that the wizarding world in the Harry Potter side of the fanfiction might see Naruto as a new threat similar to Voldemort. So, some powerful wizards could come to the Naruto world to stop Naruto from becoming too much like Voldemort, thus making them the antagonists in this strange crossover fanfiction.

It could be a character who wants to steal Brook's musical powers. Maybe a dark wizard from a third world who has heard of Brook's ability to control people's emotions with his music. He sees Naruto as an obstacle in his way to getting to Brook.

It could be a rogue ninja who has always been envious of Naruto's popularity and power. He sees the Purge as the perfect chance to get rid of Naruto once and for all and take over the Hidden Leaf Village. He might form a group of like - minded ninjas who are also tired of living under the rules and want to create their own chaos during the Purge.

Another option could be an evil wizard in the Cinderella world who sees Naruto as a threat to his control. He might try to keep Cinderella in her oppressed state to prevent her from getting closer to Naruto, who has the potential to bring new ideas and power that could undermine the wizard's authority.

Maybe a rogue ninja who has somehow tapped into dark powers related to Kami's domain. This ninja wants to use these powers to take over the ninja world, and Naruto, with Kami's help, has to stop him. In this fanfiction, the rogue ninja could have some personal vendetta against Kami as well, which adds more depth to the story.

It could be Kaguya Otsutsuki. Since she has powerful abilities and a thirst for power, she would see Kefla's power as a threat and Naruto's influence as something to be eliminated. She might try to manipulate events to turn the ninja world against Kefla and Naruto.

It could be someone who doesn't want Sakura to become stronger. Maybe a rogue ninja who fears that a more powerful Sakura would be a threat to his plans. This antagonist might try to disrupt Naruto's training of Sakura by setting up various traps or distractions.