One way a Danmachi - Fate fanfiction crossover could function is through the concept of parallel universes. The two universes could be connected in some way, and certain events could cause portals to open between them. In this scenario, the adventurers from Danmachi would enter the Fate world. They would be faced with the complex politics and power struggles there. The Fate characters might view the Danmachi characters as strange new entities. There could be a lot of misunderstandings at first, but as they get to know each other, they could learn from each other's strengths. For example, the Danmachi characters could learn about the strategic use of Command Spells from the Fate characters, while the Fate characters could be impressed by the physical combat skills of the Danmachi adventurers.
The crossover could work if there was a common goal. For instance, a powerful and ancient evil that threatens both universes. The Shinju could be the key to stopping this evil. The Justice League, with their different powers like Wonder Woman's combat skills and Aquaman's control over the sea, could bring a different perspective and set of abilities. Naruto and his friends, with their ninja training and knowledge of chakra, could also contribute. They could learn from each other. For example, Naruto might be amazed by the Justice League's technology and the League could be intrigued by the concept of chakra.
One way it could work is through a common enemy. Suppose there's a dark force that threatens both the wizarding world of Harry Potter and the world of Hotel Transilvania. The characters from both universes would have to team up to defeat it. The wizards could bring their knowledge of spells and magical defenses, while the creatures in Hotel Transilvania could use their unique physical abilities. It would be a story full of action and cooperation between very different characters.
In a Naruto and Hachishakusama crossover fanfiction, it could work by having the two different mythologies or concepts collide. For instance, the chakra system in Naruto could interact with the dark and mysterious powers of Hachishakusama. Maybe Naruto's positive chakra could have an effect on Hachishakusama's negative and spooky essence.
Well, one way it could work is if Naruto somehow enters the world of Middle - earth where Smaug exists. Maybe through some kind of magical portal. Naruto's ninja skills like his shadow clone jutsu could be used in interesting ways. For example, he could send clones to distract Smaug while he tries to find a weakness in the dragon's defenses. His speed and agility as a ninja would also give him an edge in combat against the huge and somewhat lumbering Smaug.
It could work if we consider the power systems. The Matrix has the power of the One, who can manipulate the code of the Matrix. In Naruto, there are jinchuriki like Naruto who have great power. If Naruto were to enter the Matrix, his chakra and the Nine - Tails' power could potentially interact with the Matrix's code. He might be able to break through the digital barriers or even rewrite parts of the Matrix code with his chakra, just like how he can use his chakra to perform powerful jutsu in his own world.
Well, it could work by having a magical or technological portal that connects their two worlds. Jinx could be curious and step through it into the Naruto world. Then, the story could revolve around the culture shock for Jinx and how the Naruto characters react to her strange appearance and explosive devices.
A possible way for a DBZ and Evangelion crossover fanfiction to work is in the realm of character interactions. Consider Vegeta and Shinji. Vegeta is all about pride and power, while Shinji is often insecure. Their meeting could be a clash of personalities. Vegeta might look down on Shinji at first, but then as they face a common enemy, like an Angel from Evangelion that has some sort of connection to a DBZ villain, they start to understand each other. Also, the technology in Evangelion could be something that the Z - Fighters are interested in. For example, the entry plug system could be something they study to improve their own space travel or combat capabilities.
In a Naruto and fem Goku crossover fanfiction, it could work by having a common threat that brings them together. For instance, an ancient evil that has the power to destroy both the ninja world and the Dragon Ball universe. They would then combine their unique powers and strategies. Naruto with his shadow clones and jutsu, and fem Goku with her Super Saiyan forms and energy blasts.
Well, a simple way could be through a portal. Imagine a magical portal opening between the mutant world and the wizarding world. Magneto steps through and is immediately in Hogwarts. The students and teachers are both fascinated and terrified. Harry Potter, being the brave one, approaches Magneto to find out his intentions. This encounter could spark a whole series of events where they either become friends or enemies depending on how Magneto reacts to the wizarding world's power structure.
Well, it might be possible if the Leverage crew gets pulled into the Walking Dead world somehow. Maybe they start out thinking they're on just another job, but soon realize they're in a world full of zombies. They could use their talents for planning and deception to help some of the main characters from The Walking Dead. For example, Eliot could use his fighting skills to protect against walkers while Hardison could figure out how to get communication systems working again in the midst of the chaos.