A more complex story could be that there is a prophecy in both universes that only Naruto and Ashe together can fulfill. This prophecy is related to saving all the worlds from a great darkness. They initially don't trust each other, but as they go on a journey to understand the prophecy better, they start to respect and rely on one another. Along the way, they encounter different characters from both universes who either help or hinder their progress.
One idea could be that Naruto is somehow transported to the League of Legends universe where he meets Ashe. They could team up to fight a common enemy, like an evil sorcerer who is threatening both the Hidden Leaf Village and Ashe's tribe. Naruto's ninja skills combined with Ashe's archery and leadership would make for an exciting adventure.
A fanfiction could focus on a power struggle between Ashe and Basch. Maybe there's a powerful artifact that grants great power, and both have different ideas on how it should be used. This could lead to an interesting conflict and character development as they each try to persuade the other to their side.
One idea could be to explore Naruto's life if he had been trained by a different sensei from the start. For example, if he was trained by Kakashi in a more intensive and specialized way, his skills might have developed differently. Another idea is to write about Naruto's life during a time skip where he goes on a secret mission that changes his perspective on the ninja world. Or you could focus on Naruto's relationships, like if he had a falling out with Sasuke much earlier and how that would have affected his growth as a ninja and a person.
One idea could be a what - if scenario where Naruto becomes a rogue ninja. This would completely change the dynamics of the story and his relationships. For example, he might be hunted by his former friends, and we could explore his inner struggle and reasons for turning rogue.
A story could revolve around an Anbu agent who loses his mask during a mission. As he tries to retrieve it, he has to face his own identity without the mask's anonymity. It could explore how the mask is not just a tool for concealment but also a part of his psychological armor.
One interesting idea could be the combination of Naruto's ninja skills with mecha technology. For example, Naruto might use his chakra to power up the mecha in unique ways. Another idea could be the new enemies that are created specifically for this mecha - Naruto concept, like robotic shinobi that require different combat strategies compared to normal foes. Also, the design of the mecha Naruto itself can be really cool, perhaps with features inspired by the Nine - Tails.
A fanfiction could involve a power - swapping scenario. The Powerpuff Girls get some of Naruto's chakra powers and Naruto gets a taste of their superpowers. This leads to a lot of comical and also intense moments as they try to figure out how to control these new powers. Naruto might struggle with the girls' more 'girly' powers at first, while the Powerpuff Girls have to deal with the complexity of chakra control.
A cool story could be about a Pokemon team formed by Naruto and his comrades to save both the Naruto and Pokemon worlds from a common threat. This threat could be an evil organization that is using some sort of jutsu - like power to control Pokemon and cause chaos. The team would have to travel across different regions in the Pokemon world, gathering allies and powerful Pokemon to fight against this threat. They might also discover new forms of Pokemon that are related to the chakra in the Naruto world.
There could be a fanfiction where Naruto's black hair is what attracts a new, mysterious character. This character believes that Naruto's black hair is a sign of a prophecy. So, they start to follow Naruto around, and through their interactions, Naruto learns more about himself and the world around him. For example, this character might be from a far - off land where black hair is extremely rare and is seen as a symbol of great destiny.
For Naruto alternate story fanfiction, an interesting plot could be centered around the idea that all the tailed beasts are actually sentient beings with their own goals and desires, and they choose to work with the ninja instead of being forced into submission. So, Naruto doesn't have to fight to gain their friendship. Another plot could be that the Uchiha clan never gets massacred. Instead, they work with the village to develop new and powerful jutsu. And a different idea is that Rock Lee discovers a way to use chakra without relying on ninjutsu or genjutsu, which completely changes the way he is perceived in the ninja world.
Maybe a story where Alucard, Naruto, and a character from DxD end up in a strange new dimension. Naruto uses his ninja skills to scout the area, Alucard provides protection with his vampiric abilities, and the DxD character uses their own powers to try and find a way back home. Along the way, they have to face new and dangerous enemies that are a mix of all three universes.