Some fanfictions merge the universes by having a common enemy. This enemy might be threatening both the demigod world and the ninja world. So, characters from Percy Jackson and Naruto have to team up. They bring their own unique skills and cultures, like the use of demigod powers and ninja jutsu, which then blend the two universes together as they fight side by side.
Another way is when a character from one universe is sent to the other on a quest. Let's say Percy Jackson is sent to the Naruto world to retrieve an object that has somehow ended up there. His presence then starts to mix the two universes as he befriends the ninjas and they learn about his world.
Well, in many fanfics, they merge the universes by having some sort of magical or scientific accident. For example, in one fanfic, a portal opened up between Camp Half - Blood and the Young Justice headquarters. The female Percy Jackson then gets sucked into the Young Justice world and has to adapt.
Well, in fanfiction, it could also be that there is a common enemy. For example, a powerful ancient being that is a threat to both the demigod world of Percy Jackson and the world that Agents of Shield operates in. This would force them to team up. Percy's powers like controlling water could be really useful in some of the situations that Agents of Shield faces, like dealing with underwater threats or putting out fires in a unique way.
Writers often start by establishing how a fem Percy Jackson could end up in the Harry Potter universe. Maybe through a magical portal or some kind of cross - dimensional spell. Then they find ways to make her demigod powers interact with magic. For example, her ability to control water might have an unexpected effect on a magical water - based spell in Hogwarts.
One way they could merge is through a magical portal. Imagine if the demigods from Percy Jackson's world accidentally stumble upon a portal that leads them to Westeros. They might bring their unique powers, like Percy's control over water, and it would disrupt the power balance in Game of Thrones. For example, they could help in battles against the White Walkers, using their god - given abilities. This would change the whole course of the Game of Thrones story.
Sometimes, it's a shared enemy that brings the two universes together. Maybe there's a super - powerful demon that is causing problems in both the world of the Winchesters and in Mystic Falls. So, the hunters from Supernatural and the characters from Vampire Diaries have to team up to fight it. This allows for a lot of interesting character interactions and new plot developments.
In fanfiction, they often merge through the concept of interdimensional travel. For example, a portal might open that transports the Transformers to the Star Wars galaxy. Then, they start interacting with the different species and factions there.
In such a crossover fanfiction, the universes could blend through shared quests. For instance, a new evil force that is interested in both the power of the Juubi and the powers of the Greek gods. Naruto and Percy would be brought together to fight this common enemy. Along the way, Naruto would introduce things like chakra and ninja tools to Percy, while Percy would show Naruto things like the Camp Half - Blood and his sword Riptide. This way, their universes would gradually merge.
Some fanfictions use a device or an ancient artifact as the means of merging the universes. It could be a powerful crystal that has the ability to connect different dimensions. Once this item is activated, it starts to bring elements of the Voltron and Young Justice universes together, causing characters to meet and stories to intertwine.
In many RWBY Space Marine fanfictions, they merge the two universes by having a portal or some sort of interdimensional rift. This allows the Space Marines to end up in the RWBY world. For example, in 'The Astartes of Remnant', a warp - like portal sucks in a group of Space Marines and drops them right into the middle of Vale.
The two universes blend in various ways. In fanfiction, Percy's powers can be adapted to the Skyrim setting. His ability to control water can be used in Skyrim's many waterways. Also, the mythology of Percy Jackson can be merged with Skyrim's lore. For example, the gods in Percy's world could be compared or even interact with Skyrim's divines.