Who could be the main antagonists in a 'naruto monster king fanfic'?

Maybe the Hidden Leaf Village elders could turn into antagonists. They might fear Naruto's new power as the demon king and try to undermine him. They could form alliances with other villages to try and take down Naruto. Also, there could be some new, unknown powerful forces that emerge because of Naruto's transformation. These could be ancient evils that were once sealed away but are now awakened by Naruto's new demonic presence.

It could be the Akatsuki. Even though Itachi was once part of them, now that he has the power of a Jinchuriki, they might see him as a threat. They could want to capture him to either extract the tailed beast or to stop him from using its power against them.

It could be a group of rogue ninjas who want to capture the dragons for their power. They might be led by a powerful and greedy ninja who sees the dragons as a means to gain ultimate power over the ninja world.

Another possible antagonist could be a character from Naruto's own world who has also been brought to this new world and has been corrupted by the power of the Witch King. This character might envy Naruto's new - found power as the Witch King and wants to take it for himself. So, he teams up with the dark forces in this new world to oppose Naruto, creating a lot of challenges for Naruto to overcome.

The White Walkers could be major antagonists. Naruto would have to use his skills to combat their undead hordes. Their magic is very different from the chakra - based abilities Naruto has, so it would be a great challenge.

The Akatsuki could still be a major antagonist. Even if Naruto is emperor, they might oppose his rule as it goes against their own goals of chaos and obtaining the tailed beasts.

One possible antagonist could be a jealous noble from Naruto's own kingdom who feels that Naruto doesn't deserve the prince title. This person might try to undermine Naruto at every turn, spreading false rumors about him or trying to sabotage his diplomatic efforts.

Another possible antagonist could be a fellow inmate who has a personal vendetta against Naruto. Maybe this inmate was once on the wrong side of Naruto's actions outside the prison and now sees this as an opportunity for revenge. He could try to undermine Naruto at every turn, from spreading false rumors about him to physically attacking him when the guards aren't looking.

Another option could be Orochimaru. He has his own motives and is always looking for power. He could be the head of a powerful gang in the criminal underworld of the Naruto world. He would constantly be trying to capture Naruto or his friends to use them for his experiments or to gain more power over the ninja world.

The Akatsuki could still be the main antagonists. They might be interested in Naruto's tails for their own dark purposes, like using their power to create a super - weapon or gain control over the ninja world. Another option could be a secret group of rogue ninjas who have a vendetta against the Uzumaki clan and see Naruto's tails as a symbol of their power that they want to destroy.