To start an allen walker crossover fanfic, you need to have a clear goal for the story. Let's say it's a crossover with the One Piece world. Allen might be searching for a Devil Fruit that can help him in his fight against the Millennium Earl. Make a list of the key elements from both universes that you want to include. Then start with an engaging opening scene, like Allen arriving on the Grand Line and immediately facing a threat that requires both his skills and the help of the Straw Hat Pirates.
First, choose the world you want to crossover with. For example, if it's the Bleach universe, research the rules and characters of Bleach. Then, think about how Allen Walker would fit into that world. What would his role be? After that, create an interesting plot. Maybe Allen has to help Ichigo defeat a new kind of enemy that has the powers of both Hollows and Akumas.
Begin by outlining the basic concept. If you're crossing over with the Pokémon world, consider how Allen's powers would interact with Pokémon. He could be on a journey to find a special Pokémon that has the ability to enhance his anti - Akuma weapon. Start writing down character interactions. How would Ash and his friends react to Allen? Write short scenes to get a feel for how the crossover will work.
Then, think about the plot. Consider how Noah's character traits will interact with the new elements. For example, if it's a crossover with a detective story, how will Noah's skills contribute to solving the mystery? You need to plan out the main events, the conflicts, and the resolution. Also, don't forget to create a good opening to hook the readers.
A crossover with the world of Fullmetal Alchemist would also be cool. Allen could meet the Elric brothers. His Exorcist abilities might be seen as a form of alchemy by some in that world. They could all work together to uncover a conspiracy that involves both the Homunculi and the Millennium Earl.
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.
First, decide which other universe or story you want to cross the Akatsuki with. Once you've made that choice, research both the Akatsuki and the other world thoroughly. Then, come up with a basic plot idea. For example, if you're crossing with 'Harry Potter', maybe the Akatsuki are after a powerful magical artifact in Hogwarts. Next, create some initial character interactions. How would Sasori react to seeing a wizard use magic? After that, start writing your first draft, don't worry too much about making it perfect at first.