One idea could be a story where Naruto discovers a dragon egg similar to those in the Eragon and Dragonriders universes. As he nurtures the egg, he starts to develop a connection with the dragon inside, much like how Eragon did. This could lead to Naruto having to learn new skills related to dragon riding and magic, while also facing challenges from his own world and the new elements brought in from the other two universes.
Perhaps a fanfiction where the worlds of Naruto, Eragon and Dragonriders are merged. Naruto, with his ninja skills, has to compete with Eragon and the dragonriders in a grand tournament. The tournament could involve tests of both physical combat skills (like Naruto's jutsu) and dragon - related skills (such as flying and dragon magic). This would force all the characters to learn from each other and adapt to the new and different fighting styles.
In a fanfic, Dark Naruto could team up with Eragon. Dark Naruto's combat skills and dark chakra could be combined with Eragon's dragon - riding and magic abilities. They could face challenges like an ancient evil that has been awakened and is causing chaos in both their realms. This would lead to interesting battles and character development as they learn from each other.
In a fanfiction, the chakra system from Naruto could interact with the magic in Eragon and Dragonriders in interesting ways. For instance, the dragonriders' magic that allows them to bond with dragons could be related to chakra control. Naruto's ability to manipulate chakra could potentially be used to enhance or even modify the dragon - bonding process. Eragon's magic, which is more complex and related to ancient languages, could be combined with Naruto's jutsu - based magic. For example, Naruto could learn to use Eragon's magic by inscribing the ancient languages on his ninja tools, and the dragonriders could use chakra to boost their dragon's speed or strength.
One idea could be to have characters from Naruto end up in the world of Danmachi. For example, Naruto himself could find his way into the dungeon and his ninja skills would be put to the test against the dungeon monsters. His shadow clone jutsu could be used in interesting ways, like sending clones into different dungeon levels to scout or fight. Another idea is to have the concept of chakra introduced into the Danmachi world. This could change the way adventurers fight and level up. Maybe some of the Naruto characters could train the Danmachi adventurers in new combat techniques.
One idea could be a crossover where Naruto is somehow transported to the Star Wars universe and meets Padme. Maybe he uses his ninja skills to protect her from the Sith.
Another concept is that Naruto is sent to Middle - earth. There, he could use his ninja skills and chakra powers. He and Gandalf could team up to fight Sauron. Naruto's ability to make friends and inspire others would be really useful in uniting the different races of Middle - earth against the common enemy.
A more complex idea is that the Matrix is used to create a virtual training ground for the shinobi. They enter the Matrix to practice their skills in a more controlled environment. However, they soon realize that there are some dark secrets within the Matrix, and Naruto has to lead the way to uncover the truth and free those who are trapped inside.
Another possibility is that Naruto visits the Townsville, the city where the PPG live. He might be confused by the modern technology there compared to his own world. The PPG could teach him about it while he shows them some of his ninja skills like tree - climbing and water - walking.
A third idea could be a story where Naruto's clones are mistaken for some kind of superpower by the Thundermans. Max might be intrigued and try to figure out how to do it himself. Meanwhile, the Thundermans could teach Naruto about modern technology which he has never seen in his own world. This could lead to some really interesting and comical situations as they try to understand each other's worlds.
Another possibility is that Pokemon exist in the Naruto world. Some ninja could have Pokemon as partners instead of traditional ninja animals. For example, Sasuke could have a Dark - type Pokemon like Umbreon that would match his cool and mysterious personality. And the Pokemon battles could be incorporated into the ninja battles, adding a new layer of strategy.
One idea could be a crossover where Naruto characters gain the abilities of Needless characters. For example, Naruto could get the power of Adam Blade's regeneration. It would be interesting to see how he uses it in battle, especially against tough foes like Pain or Madara.