Well, perhaps a group of outcast ninjas who have been mistreated by the major villages join forces. They develop a new and powerful fighting style that no one has seen before. They start by infiltrating the smaller villages, taking them over quietly, and then use the resources and manpower of those villages to launch a full - scale attack on the larger ones, aiming to take over the entire Naruto world.
A time - traveling villain could be an interesting concept. This villain comes from a future where the Naruto world is in ruins due to some great disaster. He travels back in time with the knowledge of future events and powerful future - era jutsu. He decides to take over the world in the past to prevent the disaster from happening in the first place, but his methods of taking over are extreme and involve subduing all the powerful shinobi clans and villages.
Well, one interesting idea could be the unique powers that come with the demon takeover. For example, the main character might gain super strength or the ability to control certain elements. Another aspect could be the internal struggle the character faces when the demon influence starts to take over their mind.
One idea could be Naruto as a street artist in a modern city. He uses his ninja skills to create amazing and fast art, like how he throws kunai, he throws paintbrushes to make unique patterns. Another is having Sasuke as a corporate spy, using his Sharingan to gather information secretly in high - tech business meetings.
One idea could be that Naruto characters are transported to the World of Warcraft universe. They could form alliances with different races like the Night Elves, with Naruto's ability to befriend others coming in handy. Another could be that the chakra system in Naruto somehow interacts with the magic in WoW, creating new and powerful spells.
One idea could be that Naruto arrives in a world full of magic. He tries to understand and master the new magic system using his ninja skills as a base. For example, he might find that his chakra control can be adapted to control magical energy in a unique way.
Madara Uchiha is another obvious candidate. Even though he was defeated in the original story, in a fanfic he could be resurrected with even greater power. His Sharingan abilities and his knowledge of the ninja world's secrets would make him a formidable antagonist for taking over the Naruto world. He could manipulate different clans and villages against each other before making his move to take over.
An interesting plot idea for Naruto fanfic might be to focus on the life of a minor character. For instance, what if we told the story of a genin who never made it to be a chunin but still had a significant impact on the village in some other way? Or a story where all the ninja abilities are suddenly switched among the characters, and they have to adapt to these new powers while still facing their usual enemies. This could lead to some really fun and unexpected character interactions.
One idea could be a modern - day person suddenly being transported into the Naruto world and having to learn chakra control from scratch. They could struggle with the cultural differences and make friends with some of the original characters like Naruto or Sakura while trying to find a way back home.
One idea could be exploring the backstories of the minor characters in the 'a dead world'. Maybe there was a character who had a pre - apocalypse profession that could be crucial in the new dead world, like a scientist who is now trying to find a cure for the cause of the dead world. Another plot could revolve around a group's journey to a rumored safe haven. They face various challenges on the way, including different types of undead and rival survivor groups.
One interesting idea could be a Sith taking over a Jedi's body. This would create a great internal conflict as the Jedi's values clash with the Sith's dark intentions. It could also lead to a very different kind of story arc within the Star Wars universe.
One idea could be that Naruto is somehow transported to Smallville. He could use his ninja skills to help Clark Kent deal with some of the more dangerous villains in Smallville. For example, when Clark is having trouble with a kryptonite - enhanced foe, Naruto's speed and combat skills could come in handy.