One idea could be that an alien race discovers the ninja world. They are intrigued by the chakra system and want to study it. Naruto and his friends initially see them as a threat but then realize they can learn from each other. For example, the aliens might have advanced technology that could be used to enhance the ninja tools.
Maybe the aliens are fleeing from a greater enemy and seek refuge in the Hidden Leaf Village. Naruto, with his big - hearted nature, decides to help them. This leads to a cultural exchange where the ninjas learn about the alien's unique abilities like telepathy, and in return, they teach the aliens about ninjutsu. It could create a whole new set of adventures and challenges for Naruto and his comrades.
First, do some research on both Naruto and the concept of aliens. Decide on the type of alien, like whether they are humanoid or completely different in form. Then, think about how the two worlds will collide. For example, will the aliens come to the Naruto world or vice versa? Next, create a plot that involves the main characters from Naruto interacting with the aliens in a meaningful way. Don't forget to keep the personalities of the Naruto characters intact.
One idea could be that a Predator ship crashes near Konoha. Naruto, being the curious and brave ninja he is, investigates. The Predator technology could be something that both intrigues and challenges the ninja world. Maybe Naruto has to learn new ways to fight the Predator's advanced weaponry while also trying to communicate with it in his own Naruto - like way.
Another concept is that a common enemy forces Naruto and Hellboy to team up. This enemy could be a powerful being that has the ability to disrupt both the ninja world and Hellboy's world. Naruto's jutsu and Hellboy's brute strength and Right Hand of Doom could be combined in creative ways to fight this foe.
Another possibility is that a villain in the Naruto world tries to use Nunnaly for her unique knowledge or skills. The shinobi of the Hidden Leaf, including Naruto, would then have to protect her. In the process, Nunnaly could learn about the values of the shinobi world like loyalty and perseverance.
One idea could be that Ichigo and Naruto are brought together by some sort of interdimensional rift. They initially don't understand each other's powers but soon realize they share a common goal of protecting their friends and worlds. They could team up to fight a powerful enemy that threatens both their universes.
One idea could be that Guts from Berserk is somehow transported to the Naruto universe. He could encounter Naruto and his friends. Maybe they initially mistake him for an enemy because of his intimidating appearance and weaponry. But as they get to know him, they realize his noble heart and his fight against the forces of evil in his own world, and they team up to face a common threat in the Naruto world.
One idea could be that the Tenno from Warframe are summoned to the Naruto universe during a great war. They could use their advanced technology and unique abilities to help the ninja clans. For example, the Excalibur could use his Radial Javelin ability to clear out large groups of enemy ninjas, much like a powerful ninjutsu.
One idea could be that Naruto is somehow transported to the world of Maleficent. He might initially be seen as a strange being. Maleficent, being curious, could decide to keep an eye on him. Naruto, with his positive attitude, might try to befriend Maleficent and show her a different way of looking at things, perhaps changing her view on humans.
One idea could be that Naruto is somehow transported to the Zootopia world. He might initially struggle to adapt to the animal - only society but his ninja skills would soon come in handy. For example, he could use his shadow clone jutsu to help solve a mystery in Zootopia, like a string of disappearances that the Zootopia police are having trouble with.
One idea could be that some of the NCIS agents are sent on a mission to a world that has similarities to the Naruto universe. They could team up with Naruto and his friends to solve a mystery that involves both their worlds, like a powerful weapon that could disrupt both dimensions. The NCIS agents would be shocked by the ninja skills and chakra usage, while Naruto and his friends would be intrigued by the advanced technology of the NCIS.