Another concept is that a character from Princess Mononoke, like San, somehow ends up in the Naruto universe. She might initially be seen as a threat because of her wild nature, but Naruto could try to understand her and they could team up against common enemies like Orochimaru who is always after power and would likely be interested in the magic of the Princess Mononoke world.
Perhaps there could be a fusion of chakra and the magic in the Princess Mononoke world. Naruto could learn to use the natural energy in that world in a way similar to how he uses chakra. This would give him new powers and abilities that he could use to fight against the industrial forces that are trying to destroy the forest in the Princess Mononoke world.
One idea could be that Naruto is transported to the world of Princess Mononoke. He could use his ninja skills to help Ashitaka in his quest. Maybe Naruto's ability to make friends easily would allow him to form alliances with the different tribes in that world, like the forest spirits and the humans at Iron Town.
One idea could be that Naruto is somehow transported to the world of Zelda. He could use his ninja skills to help Zelda in her fight against Ganon. For example, his shadow clone jutsu would be very useful for creating distractions or for gathering information in different areas of Hyrule at the same time.
One way the worlds could merge is through a magical portal. Maybe a Hogwarts student accidentally discovers a portal that leads to the world of Princess Mononoke. The student could then introduce magic from the Harry Potter world to the people in Mononoke's world, like using spells to heal the forest spirits that are sick or injured. Another aspect could be the sharing of beliefs. The respect for nature in Princess Mononoke's world could influence the wizards in Harry Potter to be more in tune with the natural magic around them.
Well, there might be some out there. However, 'Yaoi' often involves male - male romantic or sexual relationships, which might not be everyone's cup of tea. In the Naruto and Princess Mononoke universes, it's a very niche area of fanfiction. You could try searching on some large fanfiction platforms, but be aware that the quality can vary greatly.
Well, Naruto is a very energetic and positive character. He would probably be in awe of the forest spirits in Princess Mononoke at first. He might try to befriend them immediately. And when it comes to San, he would likely respect her connection with the forest and try to understand her motives. For the characters in Princess Mononoke, they would be quite surprised by Naruto's strange abilities like his Rasengan. Ashitaka might see Naruto as a potential ally in his journey to find a balance between the humans and the forest.
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.