A fanfiction could be about a prophecy that involves both Naruto and Powergirl. In order to save both their universes, they must find a way to combine their powers. This leads to a journey where they face many challenges, both internal and external. Naruto has to deal with his own insecurities about being in a new and strange place, and Powergirl has to learn to trust Naruto completely.
Well, a frequent theme is the idea of teamwork. Given their different skill sets, fanfictions often have them teaming up to face a powerful foe. For instance, they might combine Naruto's strategic thinking in combat (learned from his ninja training) with Powergirl's brute force. Also, the theme of mutual respect can be seen, as they learn to appreciate each other's abilities and backgrounds over the course of the story.
One idea could be that Powergirl somehow gets transported into the Harry Potter universe. She could use her super strength and flight abilities to help the students at Hogwarts during a time of great danger, like when Voldemort is on the rise. Maybe she teams up with Harry, Hermione, and Ron to fight the Death Eaters in a unique way that combines magic and her superpowers.
Another storyline might focus on the relationships between the Sand ninja and the Leaf ninja. For example, how they overcome their past differences and work together on a mission. It could involve a lot of character development and understanding between different cultures in the Naruto universe.
One interesting storyline could be a crossover where Naruto somehow ends up in Hippolyta's world. He might use his ninja skills to help the Amazons in their battles, like using his shadow clone jutsu to create distractions during an enemy attack.
Another storyline might involve Koharu being in danger and Naruto coming to her rescue. In the process, they discover a hidden bond between them that was previously unnoticed. Maybe they find out that they are related in some long - lost way or they just develop a deep friendship that changes the way the village views their relationship.
One interesting storyline could be exploring the backstories of minor characters in the Naruto universe. For example, how a random villager in Konoha came to be there and their family history.
One interesting storyline could be where Naruto and Izumi meet during a mission outside of Konoha. They initially have some misunderstandings due to their different upbringings, but as they work together, they start to understand each other better. Another could be a story set in an alternate universe where Naruto is not from Konoha and Izumi is sent to find him. They end up on a journey together, facing various challenges and growing closer along the way. A third one might be a time - travel story where Izumi goes back in time and meets a younger Naruto, and she tries to change the future for the better by influencing him early on.
Some fanfictions focus on Naruto having a different upbringing. For instance, if he was raised by a different clan, like the Hyuga. This would give him access to their unique abilities and fighting styles. He could also have a different set of friends and rivals, which would completely reshape his character development and the overall plot of the story.
One interesting storyline could be about Naruto having a new and powerful jutsu that he discovers in a flash of inspiration. This jutsu might be related to his chakra nature in a unique way. Another could be a fanfiction where Naruto travels back in time in a flash of some mysterious power and has to relive parts of his past with his new knowledge. There could also be a story where Naruto meets a new character who has a special connection to the flashy, yet dangerous, forbidden jutsus.
One interesting storyline could be Naruto finding himself in the Digital World where he meets Angewomon. They could team up to fight a new threat that is endangering both the real world and the Digital World. Maybe Naruto's ninja skills and Angewomon's powers combine in unique ways to defeat enemies.