Another approach is to have characters from one universe cross over to the other. Maybe Darth Vader could end up in Gotham. His imposing presence and dark powers would be a huge shock to the criminals there. He could even form an unlikely alliance with Batman, with Vader's goal being to find a way back to his own universe while Batman tries to keep Gotham safe from this new, extremely powerful threat.
One way to merge the two universes in fanfiction could be through a plot device like a dimensional rift. For example, a Sith Lord could accidentally open a rift that leads to Gotham City. This would bring the dark and brooding atmosphere of The Dark Knight into the Star Wars universe. Batman might find himself in a world of lightsabers and the Force, and his detective skills could be put to the test in a whole new way.
In fanfiction, it could also be interesting to explore how the concepts of the Force and the Dark Side compare to the morality in Gotham. The Jedi's code of honor could be contrasted with Batman's no - killing rule. A character like Luke Skywalker could come to Gotham and try to inspire the people there with his Jedi teachings, while also learning from Batman about how to fight crime in a more 'grounded' way.
In a Naruto x Star Wars Rebels fanfic, the two universes could be merged by exploring the idea of different cultures. The diverse cultures in Naruto, like the Hidden Villages, could be compared to the various planets and species in Star Wars. For instance, the Hidden Leaf Village could be seen as a planet in the Star Wars universe. The values and traditions of each could be shared. The Rebels' fight for freedom could be paralleled with the ninja's fight for their villages. This would allow for a deeper exploration of themes such as loyalty, friendship, and the struggle against oppression in both universes as the characters from Naruto and Star Wars Rebels interact and influence each other.
One way could be through a magical portal. Imagine in a fanfic, a powerful mage in the Game of Thrones world accidentally opens a portal to the Naruto universe. Dark Naruto, with his edgy and powerful nature, could be seen as a threat similar to some of the dark forces in Game of Thrones. He might form an alliance with a power - hungry lord in Westeros, thinking he can use their resources to achieve his own goals in the Naruto world. For example, if he teams up with Littlefinger, they could plot to take over both kingdoms using Dark Naruto's powers and Littlefinger's cunning.
Another approach could be a shared enemy. Suppose there is an entity that exists in both universes in a different form. Writers could create a story where the characters from Highschool DxD and Prototype have to team up to defeat this entity. This would require them to understand each other's powers and work together, leading to a lot of character development and exciting action scenes.
Well, it might involve the political intrigue. The complex politics in Game of Thrones could be combined with the NERV organization's secrecy in Evangelion. Maybe the different houses in Game of Thrones are vying for control over the Evangelion units. And the pilots of Evangelion could be seen as pawns in this political game, just like many characters in Game of Thrones are used by the powerful lords.
You could also have a character who has a connection to both universes. Maybe a half - Naruto - half - Angeloid being. This character would act as a bridge between the two worlds. They would introduce the concepts of one universe to the other. For example, they could teach the ninja in Naruto's world about the advanced machinery of the Angeloid universe and at the same time show the Angeloid the importance of things like honor and loyalty in the ninja world. As this character moves between the two universes, the two start to blend together more and more.
Another possibility is that a character from the DxD universe, perhaps someone with a strong sense of adventure, accidentally stumbles into the SPD universe. This character could then form an alliance with the Power Rangers and start to introduce elements of their home universe, gradually leading to a more integrated scenario where the two universes start to merge on a larger scale.
In fanfiction, it could be that the technology of Gundam Seed Destiny is introduced into the Naruto world. The ninja villages could start using Gundam - like mechas in their battles. This would completely change the power balance. The shinobi would need to adapt to this new form of warfare. Also, the pilots from Gundam Seed Destiny could find themselves in the Naruto world and learn about chakra, and they might try to combine their piloting skills with chakra - based attacks.
It could be Naruto himself. His ability to tap into the Nine - Tails' chakra gives him an incredible power boost. In the merged universe, he might be able to use the Force as well, which would make him an unstoppable force. With his speed, strength, and now potentially the power of the Force, he could easily defeat most opponents.
One way to blend the two universes could be through time travel. In a fanfiction, perhaps a character from Back to the Future accidentally travels to the Star Wars galaxy. They could introduce advanced Earth technology to the Star Wars characters, like the hoverboard, which might be used in lightsaber battles for added mobility. This would create a whole new dynamic in the Star Wars universe.
One way is by creating crossover characters. For example, a character could have the powers of a Jedi from Star Wars and also be a part of the Avengers team. Another way is to use similar story elements like a fight against a powerful and evil force. Writers can also have the heroes from both universes meet in a neutral location, like a new planet or dimension, and team up to face a common threat.