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.
A great plot could involve a character from the real world entering the Naruto world with a special ability that no one there has. For example, they might have the power to manipulate time in a limited way. This would cause a stir among the ninja clans, and they would either be hunted or revered. They could then use this ability to change the course of some important events in the Naruto world.
One idea could be Naruto being a high - school student. He might use his ninja skills secretly to help his friends out of various troubles, like bullies or difficult exams. For example, using his shadow clone jutsu to study for multiple subjects at once.
One idea could be Naruto getting trapped in the demon world and having to form alliances with different demon clans to find his way back. He could learn unique demon jutsus during his time there.
One interesting plot could be a story where Naruto discovers a hidden ancient jutsu in the fanfiction world that gives him the ability to travel between dimensions. He uses this power to visit alternate versions of Konoha and teams up with different versions of his friends to face a new, powerful enemy that threatens all the dimensions.
One idea could be Naruto arriving in a world full of magic, and he has to learn to combine his chakra skills with magic. For example, he might use his Rasengan with a magical spell to create a super - powerful attack.
One idea could be exploring the darker sides of the ninja villages that are usually hidden. For example, the corruption within the political systems of the villages. Another could be focusing on characters who have turned to the dark side due to past traumas, like a character who lost their family in a war and then joined a dark organization. Maybe also a plot where the traditional ninja values are being twisted in the 'world of darkness' version, leading to moral dilemmas for the main characters.
In some naruto alternate world fanfiction, there could be a plot where Naruto travels back in time. He could use his knowledge of the future to prevent tragedies like the Uchiha massacre. He might also be able to train with the past Hokages earlier and gain different skills. This would change the course of the entire Naruto world, and his relationships with characters like Sasuke and Sakura would be very different as a result.
One idea could be Naruto arriving in a world full of magic. He has to learn to combine his chakra skills with magic to defeat a powerful dark lord. For example, he might use his shadow clone jutsu in creative ways within magical battles.
One idea could be Naruto having to adapt to the different social norms in the female - ninja world. For example, the way training or missions are organized might be different. Maybe the female - ninjas have a more collaborative approach compared to the male - dominated world he's used to.
One idea could be that in this all - female Naruto world, the female ninjas have to deal with a new kind of threat that only targets women. They form an all - female alliance to combat it. Another could be exploring the different relationships between the female characters. For example, how Sakura and Ino's friendship might develop in a world without male counterparts, and they could be rivals in a different way, like competing for the top position in a female - only ninja academy.
A plot idea could be that Naruto discovers a new, ancient form of chakra that has been lost for centuries. He then has to train to master this chakra while also dealing with the political implications within the Hidden Leaf Village. Some elders might be against him exploring this new power for fear of the unknown, but Naruto, being Naruto, is determined to master it for the good of the village.