In some fanfictions, the brainwashing jutsu on Naruto could be part of a bigger scheme. For example, a new villainous organization wants to use Naruto as a weapon. They brainwash him and try to control his immense power. But Naruto's willpower, even under the jutsu, might start to show through in small ways, and his friends use these glimmers to figure out how to save him.
Well, he could be made to do all sorts of things against his will. Maybe he'd be forced to fight his friends. It would be a really dark turn for his character, as Naruto is known for his strong will and loyalty.
Another possibility is a new, unknown enemy. This could be someone from a far - off land who has heard of Naruto's power and developed a special brainwashing jutsu just to take over Naruto and use him to conquer other villages.
Some fanfictions might focus on the psychological effects of the mind control jutsu. For example, if a character is under mind control for a long time and then is freed, how do they deal with the memories of what they did while controlled? It could be a very emotional and character - driven story. Maybe they struggle with guilt or fear of being controlled again.
Perhaps with the help of his strong bonds with his friends. Their love and trust could be the key to snapping him out of it.
Perhaps in a fanfiction, an enemy uses death magic to bring back powerful villains from Naruto's past. Naruto then has to use his own skills and newfound knowledge of death magic (maybe learned from a wise hermit) to defeat them all over again. This could lead to some really intense battles and character development for Naruto as he grapples with this new threat.
Well, he could become extremely powerful. Maybe he'd use the forbidden jutsu to defeat powerful enemies like Madara or Kaguya in a really unexpected way. For example, if it was a time - travel related jutsu, he could go back in time and stop certain events from happening that led to the rise of these villains in the first place.
There could be a jutsu that allows for instant teleportation across long distances. This jutsu might be a new discovery in the fanfiction world, perhaps created by a character who has been experimenting with space - time ninjutsu. They might use it to quickly get in and out of battles or reach far - off places in a blink.
One possible plot could be Naruto using the Rinnegan's time - travel ability to prevent the Uchiha massacre. He could change the course of history and save Sasuke from a life of revenge.
Some fanfictions might have a plot where Naruto remembers a past life as a normal person in a non - ninja world. This would create an interesting contrast as he tries to adapt his ninja skills and values in a world that has no concept of chakra or jutsus. He could use his ninja knowledge to solve normal world problems in unique ways. Or, perhaps he remembers a past life as an enemy of the ninja world. This internal conflict between his current self who is a hero and his past self who was an antagonist could be a major plot point. He would struggle with the memories and the urge to not repeat the mistakes of his past life.
One interesting plot could be Hermione being forced to work with a Death Eater undercover. This creates a lot of tension as she has to hide her true feelings and intentions. Another might be a story where a Death Eater has a change of heart because of Hermione's influence. It shows the power of her character. And then there could be a plot where Hermione discovers a hidden group of Death Eaters within Hogwarts and has to figure out how to expose them without getting caught herself.