Who could be the main antagonist in 'The Black Death Returns Naruto Fanfiction'?

It could be a new villain who has risen to power during Naruto's absence. This villain might have a vendetta against Konoha or the ninja world in general because of something that happened while Naruto was away.

There could be a group of anti - ninja revolutionaries as the main antagonists. They see Naruto's return with the swords as a threat to their plan of overthrowing the existing ninja order. They try to take the swords from Naruto to use them as symbols of their new regime, believing that the power of the swords will help them convince other ninjas to join their cause.

A new dark entity could be the main antagonist. This entity might have been awakened by Naruto's return from the dead. It could be something that was sealed away long ago and Naruto's return breaks the seal. The entity would then target Naruto and his loved ones to prevent him from getting in its way of ruling the ninja world.

Perhaps an old enemy that Naruto thought was defeated has returned, stronger than ever. This enemy could hold a grudge against Naruto and the elemental nations for past defeats and wants revenge.

Perhaps it's an old enemy who has somehow managed to come back stronger. Maybe someone from Orochimaru's old experiments that went wrong, but instead of dying, they gained some dark and powerful abilities. They see Naruto's return as a threat to their plans of world domination, so they target Konoha first. They might be able to control dark chakra in a way that no one has seen before, and use it to create chaos and destruction. They could also have some minions who are equally as powerful and loyal to them, making them a formidable foe for Naruto and Konoha.

It could be Orochimaru. Even though he's had his moments of redemption, he might relapse into his old ways. He could see Naruto's 'death' as an opportunity to carry out some evil plan that Naruto would have stopped. Maybe he wants to use Naruto's death to create chaos and then take advantage of the power vacuum in the ninja world.

It could be an evil shinobi who has somehow managed to control or manipulate the God of Death's powers for his own malicious purposes. This shinobi might use the power to create chaos in the ninja world, like raising the dead and making them fight against the living.

It could be a powerful rogue ninja who wants to use Naruto's new - found 'harbinger of death' status for his own evil purposes. Maybe he believes that Naruto can lead him to powerful and dark artifacts that are only revealed during times of death and destruction.

It could be an evil shinobi from Naruto's world who has also ended up in the Death Parade world and is trying to corrupt the system. He wants to ensure that all the souls are sent to the void or something worse, just for his own amusement or power - hungry desires.

In this fanfiction, perhaps the Black Death returns in a form that is related to some dark jutsu gone wrong. It might start in a small village and then spread rapidly. The story could focus on Naruto and his friends trying to find a cure. They might have to travel to different places, meet new characters, and face many challenges along the way. For example, they could encounter groups who think the disease is a punishment from the gods and oppose their attempts to stop it.