Don't forget about the character development. Show how the characters from different universes grow and change as they interact. For instance, if Yoh from Shaman King is in the Fullmetal Alchemist world, he could learn about the different types of alchemy and how it's different from his shaman powers, and this could lead to his own growth as a character.
Next, create a plot that involves the main characters from both universes. It could start with a strange phenomenon that brings them together. Maybe a powerful shaman accidentally opens a portal to the One Piece world and has to team up with Luffy to get back home while also solving a problem in that world.
First, you should re - watch or re - read the Shaman King series to get a fresh feel for the characters, the world, and the story. Then, pick a concept or idea that you're really passionate about, like one of the ideas I mentioned before. Next, create an outline of your story. Decide on the beginning, middle, and end. After that, start writing the first draft. Don't worry too much about grammar or making it perfect at this stage. Just get your ideas down on paper. Once you have a first draft, you can go back and start refining it, adding more details, and fixing any mistakes.
First, familiarize yourself with the original series thoroughly. Know the characters, their powers, and the rules of the shaman world. Then, think of a unique concept. It could be a new adventure for the characters or a different take on an existing plot point.
First, decide which other franchise you want to crossover with. For example, if it's with a superhero universe, think about how the Dinosaur King characters and their dinosaurs would fit into that world. Then, create an interesting plot. Maybe the dinosaurs are needed to help the superheroes save the world from a new threat.
First, choose the fables you want to cross. Then, think about how the characters from each fable would interact. For example, if you choose 'The Ant and the Grasshopper' and 'The Fox and the Grapes', you might start with the grasshopper meeting the fox while looking for food. Just start writing down these initial ideas.
First, decide which universe you want to cross Monika into. It could be a game, a book, or a movie world. Then, research that world thoroughly. For example, if it's a 'Monika in the Star Wars' crossover, learn about the Force, the different species, and the political systems in the Star Wars universe.
First, decide which world you want to cross Elsa over with. For example, if it's the world of Narnia, think about how Elsa's powers would interact with the magic of Narnia. Then, create a plot. Maybe Elsa is called to Narnia to help the Pevensie children fight the White Witch. Just start with a simple idea and build on it.
First, decide which other show or universe you want to cross over with. For example, if it's 'The Office', think about how the characters from 'Seinfeld' would fit into the Dunder Mifflin office environment. Then, come up with a basic plot idea. Maybe Jerry has to give a comedy workshop to the office employees.
First, decide which universe you want to crossover with. Then, study the lore and characters of both Twewy and the other universe. For example, if it's a crossover with Pokemon, understand how Pokemon battles work and how the Pokeballs function. Then, think of a plot that would bring the characters together in a believable way, like a strange portal opening between the two worlds.
First, decide which other universe you want to cross 'HxH' with. Then, study the lore and characters of both universes thoroughly. For example, if you choose 'My Hero Academia', know the quirks of the 'MHA' characters and how they interact with the Nen abilities in 'HxH'. Next, come up with a basic plot like a common threat that both universes need to face together.
Begin by creating an outline. Outline the main plot points, like how the characters will meet, what their initial reactions will be, and how they'll overcome their differences to fight the common foe. If you're doing a Trollhunters and 'Lord of the Rings' crossover, you might start with the Trollhunters being transported to Middle - earth. Outline how they'll interact with the hobbits, dwarves, and elves. Then, start writing your first draft, don't worry too much about making it perfect at first.