A third concept could be a time - travel fanfiction. Bulma invents a time - traveling device and accidentally brings Naruto to the past in the DBZ timeline. There, they have to be careful not to disrupt the events that are supposed to happen. Naruto could learn from the Z - Fighters, and in return, he could teach them some of his ninja techniques. This would create a whole new dynamic between the two universes and the characters within them.
One idea could be a crossover where Bulma's technology is used in the Naruto universe. For example, she could create some new kind of ninja tools with her advanced knowledge. Maybe she helps the Hidden Leaf Village upgrade their defense systems. It would be interesting to see how the Naruto characters react to her and her inventions.
Another possibility is a story where Naruto is somehow transported to the DBZ universe. Bulma could be the first person he meets. She might initially be confused by this strange, orange - clad boy with strange powers. But then they could team up, with Naruto's ninja skills and Bulma's intelligence. They could face off against common enemies, like some of the minor villains in the DBZ world who are causing trouble in a new way that requires both their skills to stop.
A third fanfiction concept could be about how they prepare for the baby's arrival. Vegeta, not knowing much about Earthling baby things, has to learn. Bulma tries to teach him, and there are a lot of cultural clashes and misunderstandings at first. But as time goes on, they work together to create a perfect nursery and get ready for their new family member.
Another possibility is a story where Nami discovers a strange object on an island that transports her to the Naruto universe. There, she meets Naruto and they learn from each other. Nami could teach Naruto about the value of money and trading in the pirate world, while Naruto could show Nami how to master her own inner strength and use it to protect her friends more effectively. This could lead to an interesting adventure as Nami tries to find a way back to her own world with Naruto's help.
Another fanfiction concept could be that Kira is sent on a mission to the Naruto world. There, she meets Naruto and they start training together. Naruto teaches her some ninja techniques, and in return, Kira shows him how to better control his chakra using the principles of her Ranger powers.
Another fanfiction concept could be that Erza somehow ends up in the Naruto universe. She might join Naruto's team for a mission. Erza's strong sense of justice and her powerful magic would be really interesting to see in the context of Naruto's world. For example, she could use her armor magic to help Naruto and his friends in a battle against a powerful enemy.
One idea could be a crossover where Kimberly somehow gets transported to the Naruto universe. She could use her Power Ranger skills to team up with Naruto and his friends against a common enemy, like an Akatsuki member who has some connection to the forces of evil in the Power Rangers world.
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.