Well, a good way is through the use of magic or energy. In Naruto, there's chakra, and in Star Fox, there's energy sources for their ships and weapons. Writers can make it so that these two forms of power interact in interesting ways, like chakra - powered ships or energy - enhanced jutsu.
The settings can also be blended. Picture Naruto's Hidden Leaf Village in the middle of a forest on a planet in the Star Fox universe. Or the Star Fox team having to land on Naruto's world and deal with the various ninja clans and their politics. This mixing of settings provides a rich backdrop for all kinds of adventures and conflicts.
Character relationships are also key. You could have Naruto befriend a Sekirei who is out of place in the ninja world. Their friendship could grow as they help each other understand their respective worlds. This would allow for a lot of emotional depth and character growth in the story. You could also introduce conflicts based on the differences in their worlds' values. For instance, the ninja's code of loyalty might clash with the Sekirei's concept of their purpose. Resolving these conflicts can make the fanfic more engaging.
Well, the first step is to find common elements. For example, both Naruto and 2NE1 have a sense of teamwork. In Naruto, the characters rely on each other in battles, and in 2NE1, the members work together to create great music and performances. In a fanfiction, this could be emphasized by having the Naruto characters and 2NE1 members collaborate on a project that requires both physical strength and musical talent.
Magic and chakra could be combined. In the fanfiction, it could be that the power of the Chains in Pandora Hearts can be harnessed using chakra. So a character like Kakashi could figure out a way to use his Sharingan to control a Chain, creating a unique fighting style that combines the two fictional universes.
By mixing the unique abilities. Naruto's ability to use chakra can be related to the energy sources in Gundam. For instance, chakra could be used to power up a Gundam's special attacks.
To blend the worlds well, you can start with the geography. Imagine if the Viking lands were somehow connected to Westeros, perhaps through a long - forgotten sea route. Characters could then travel between the two places, bringing their cultures and ideas with them. Also, consider the religions. The Norse gods in Vikings and the Seven in Game of Thrones (or the old gods in the North) could have some sort of interaction. For instance, a Viking character could be confused by the different religious beliefs in Westeros and try to impose their own, leading to interesting conflicts and discussions.
The worlds can be blended by having the characters share their unique skills. Like Naruto teaching the 'Your Lie in April' characters some basic self - defense ninja moves, and in return, they teach him about music. For example, Kousei could show Naruto how to read sheet music.
One way to blend Naruto and Final Fantasy 15 in fanfiction could be through character crossovers. For example, Noctis could meet Naruto. Noctis has his unique combat skills with his weapons and magic, while Naruto has his ninja techniques. They could learn from each other. Maybe Noctis could teach Naruto some magic tricks, and Naruto could show Noctis how to be more stealthy like a ninja. This would create interesting interactions and new storylines.
To blend the two worlds well, start with the settings. You can create a place where both the elements of the Naruto universe like Hidden Villages and the Percy Jackson world such as Camp Half - Blood exist side by side. For example, a hidden village near a large body of water which is also a secret entrance to Camp Half - Blood. Then, for the characters, make them interact in a believable way. Naruto's curious nature would make him eager to learn about Percy's world and vice versa.
The key is to find common ground. Both have their own groups of heroes and villains. You can start by having a threat that affects both universes. For instance, a new evil force that wants to take over both Earth (where the Joes operate) and Cybertron (the Transformers' home). This forces the two groups to collaborate.
To blend the worlds well, you need to consider the characters' personalities. The serious and scientific minds of the Criminal Minds team can contrast with the more laid - back and supernaturally - aware Buffy gang. This contrast can create interesting interactions and conflicts. For example, some of the BAU members might be skeptical about the existence of vampires at first. Then, as they witness it, they have to adapt their worldviews. You can also introduce a common enemy that requires both groups to work together. Maybe a demon that is using psychological manipulation to create chaos in both the human world and the Buffyverse.