One idea could be a crossover where Naruto is transported to the world of Westeros. He meets Arya Stark and they team up. Naruto could teach Arya some of his ninja skills, like how to move stealthily like a shinobi. This would enhance Arya's ability to seek revenge on her enemies in a more efficient way.
A possible fanfiction could involve both Naruto and Arya Stark being chosen by some sort of magical or otherworldly force. They have to work together to defeat a common enemy that threatens both their worlds. Along the way, they learn about each other's cultures and values. For example, Naruto could learn about the complex family and honor system in Westeros from Arya, and Arya could be inspired by Naruto's never - give - up attitude towards achieving his goals.
Another concept is a fanfic where Sansa Stark is transported to the Naruto universe. She could find herself in Konoha and start learning about chakra and ninja skills. Naruto, being the friendly and curious type, would be one of the first to befriend her. He might teach her some basic ninja moves, and in return, Sansa could share her knowledge of court politics, which could be useful in the complex shinobi society.
In a fanfiction about Arya Stark being pregnant, she might be in a situation where she has to keep her pregnancy a secret. Maybe she's in a land where her enemies are everywhere, and if they find out, they'll use it against her. She could rely on her skills of disguise and stealth to hide her condition as she tries to find a safe place for herself and her baby.
One idea could be Arya using her Faceless Man skills to avenge the wrongs done to her family. She could infiltrate the enemies' strongholds unnoticed and take them out one by one.
A possible fanfiction could be set in an alternate universe where Tony Stark is a fallen hero and Lucifer, seeing his potential, decides to recruit him for his own purposes. Stark initially resists but as he sees the chaos around him that he can't fix with his normal means, he starts to consider Lucifer's offer. But then he remembers his past and the people he has saved, and decides to fight against Lucifer instead, using his genius to find a way to defeat the devil.
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.