A powerful dark spirit might be the main antagonist. This spirit could sense Naruto's new ability to control darkness and see him as a threat. So it starts causing chaos in the ninja world, forcing Naruto to use his dark - controlling powers to stop it. The spirit could have the ability to possess other ninjas, making them do its bidding.
Another possibility is a group of ninjas who worship the darkness. They see Naruto as an abomination because he is a well - known hero trying to control darkness. So they team up to stop him and take the power of darkness for themselves. They might have some dark rituals and forbidden jutsus that make them a formidable foe for Naruto.
It could be an ancient evil that has been lurking in the shadows for ages. Maybe a dark spirit that was sealed away long ago and is now breaking free, and Naruto has to control the darkness within himself to fight it.
It could be Orochimaru. He's always been interested in new and powerful jutsus. He might see Naruto's shadow - controlling ability as something he wants to steal or use for his own evil purposes.
It could be an old ninja who was once banished from Konoha for using dark jutsu and now wants revenge. He might see Naruto as a symbol of the village he hates and tries to corrupt him by luring him into the darkness.
It could be Orochimaru. He has always been interested in power and has no qualms about using dark methods. He might see Naruto as a perfect vessel or a tool to further his own dark plans, and through his manipulations, Naruto starts to be consumed by darkness.
It could be a rogue Huntsman who wants to use Ruby's power to control Grimm for his own evil purposes. He might believe that with the Grimm under his control, he can rule over Remnant. He would then be constantly trying to kidnap Ruby or figure out the secret behind her power, and would oppose team RWBY at every turn.
It could be another character who also has some time - related powers but uses them for evil. This character might try to steal Percy's time - controlling ability or use their own powers to disrupt the timeline for their own gain.
In 'naruto controls the darkness' fanfiction, it could also be that Naruto is exposed to a dark energy source accidentally. This energy starts to influence his thoughts and actions in negative ways at first. But being Naruto, he doesn't give in. He uses his strong willpower and the positive relationships he has with his friends like Sasuke, Sakura, and others to find a way to control this new dark power. He might have to face some of his own demons from his past, like the loneliness he felt as a child or the times he failed to protect his friends, and use these experiences to better understand and control the darkness within him.
In a 'naruto controls darkness fanfiction', perhaps Naruto initially struggles with this new power. He's a hero associated with light and positive energy, so controlling darkness could be seen as a corruption. But then he realizes he can use it for good, like infiltrating dark organizations by blending in with their dark - themed jutsus.
A group of power - hungry shinobi from a hidden village could be the main antagonists. They see the 'angel of darkness' as a weapon that they can use to gain supremacy over other villages. They start a series of attacks and schemes to capture the angel, putting Naruto and his allies in a difficult position as they try to protect it and keep the peace in the ninja world.
A powerful sorcerer who wants to control the power of the fairy of darkness for his own evil purposes could be a great antagonist. He might try to trap her and force her to do his bidding.