Some writers create a situation where the problems in the Supernatural world are related to Hermione's world. Maybe a dark wizard has escaped into the Supernatural universe and is causing chaos. Hermione then has to team up with the Supernatural characters to stop this threat. This allows for a seamless combination of the two universes, as they both have to work towards a common goal using their respective skills and knowledge.
Writers often blend the two universes by creating a common threat. For example, a demon that has ties to both the Supernatural world and the DC universe's magic or technology. They also use character crossovers, like having Dean Winchester meet Clark Kent. This allows for an exchange of ideas and values between the two different worlds.
Some writers combine the two universes by setting the story in a new location that has elements of both shows. Let's say a new town is created that has a prison - like facility but also has the normal civilian life aspects from 'Just Friends'. Characters from both shows are then brought there and their interactions are written about. This allows for new and interesting dynamics to be explored as the characters from different backgrounds have to co - exist and deal with each other's quirks and personalities.
Character crossovers are a key way. Writers will bring characters from both universes into the same story. They might have Hermione meet Bella, and through their interactions, the two different worlds start to merge. The slash aspect can then be added by creating unique relationships between characters from the two series, like a budding romance between a wizard and a vampire. This not only combines the universes but also adds an interesting new dimension to the story.
Well, one way could be through a crossover spell or some sort of interdimensional rift. Maybe a character from Twilight somehow ends up in the Naruto world and has to adapt to the ninja way of life.
Often, it combines them through crossovers. For example, a portal could open between the Naruto universe and Shinji's world, allowing characters to travel between them.
Writers can start by researching the lore of both shows thoroughly. They need to understand the rules of the 'Supernatural' world, like how angels and demons operate, and also the nature of the Wesen in 'Grimm'. Then, they can find common elements to build on. For example, both shows deal with creatures that are hidden from the normal human world. Writers can use this shared concept to create a scenario where the characters from both shows meet. Maybe a Wesen is causing trouble that has 'Supernatural' implications, so the 'Supernatural' characters get called in, and the 'Grimm' characters are already on the case.
In many 'Master Chief RWBY' fanfics, they combine the universes by having Master Chief somehow end up in the RWBY world. This could be through a portal or some kind of interdimensional rift. Once he's there, his high - tech equipment and combat training from his own universe contrast with the more magical and combat - school - based RWBY world.
One way is through power systems. The biotics in Mass Effect and the chakra in Naruto can be related. Maybe a character in a fanfiction discovers that biotics are a form of chakra or vice versa. Also, the different races in Mass Effect and the clans in Naruto can interact in terms of politics and alliances. For instance, the Uchiha clan could form an alliance with the Salarians based on their shared intelligence and strategic thinking. And the stories can also use the different settings, like having a battle take place on a Mass Effect planet but with Naruto - style combat techniques.
They can combine in terms of magic systems. In some fanfictions, the powerful and often incomprehensible magic in the Cthulhu universe might blend with the more structured magic of Harry Potter. For example, a spell in Harry Potter might be corrupted by Cthulhu's influence and become a more dangerous and unpredictable force.
It might also combine them by setting the Tetris game in the Hogwarts castle. So, instead of a plain background, you have the Great Hall or the Gryffindor common room as the backdrop for the game. The sounds of the game could be replaced with magical noises like spells being cast or the flapping of a hippogriff's wings.