A cool plot could be that Naruto is turned into a small child again, but he still has all his memories. He has to re - live parts of his life, but this time, he can use his knowledge to change things for the better. For example, he could befriend Sasuke much earlier and prevent him from going to Orochimaru. This would be a really interesting take on his character development and his relationships.
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.
The main antagonist could be a rogue ninja from a long - lost clan that has a grudge against Konoha. This ninja could have a powerful and unique kekkei genkai that makes them a formidable foe for Naruto and his friends. They might be seeking revenge for something Konoha did to their clan in the past.
One plot idea could be a character from the All for One world somehow ending up in the Naruto universe and having to adapt to the chakra system. Maybe they try to steal chakra powers like they steal quirks in their own world.
A fanfiction could be that Temari gets injured on a mission near Konoha. Naruto, being the hero he is, takes it upon himself to nurse her back to health. In the process, they share stories from their childhoods and discover they have more in common than they thought, which leads to a budding romance.
One great Naruto Temari fanfiction idea could be about them going on a joint mission in a new, mysterious land. They have to rely on each other's skills to survive and in the process, they start to realize their feelings for each other are deeper than just friendship.
One idea could be a 'Harry Potter' fanfic where the characters time - travel to different eras in the wizarding world's history. They could meet famous wizards from the past and change the course of events in small ways. Another is a 'Lord of the Rings' fanfic where the hobbits discover a new and strange magic that they have to use to save Middle - earth from a different kind of threat, not just Sauron.
One idea could be a story where Pikachu gets separated from the trainer in an unknown and dangerous area, like the mysterious depths of Viridian Forest. It has to find its way back while making new Pokemon friends and facing challenges from wild Pokemon.
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 Naruto being transported to a dimension where chakra doesn't exist, but he discovers a new form of energy and has to learn to use it from scratch. This would force him to adapt his fighting style completely.
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.