You can make it unique by creating a new power system that combines the quirks from My Hero Academia and the powers in Invincible. Maybe there's a way to fuse a quirk like Todoroki's with Mark's Invincible powers to create something entirely new and exciting for the story.
In some fanfictions, there might be a crossover where the hero academies in both universes interact. Imagine U.A. High students visiting the school in Invincible's world. This could lead to interesting exchanges of training methods and ideas about heroism. Also, characters like All Might and Omni - Man could have some intense philosophical debates about power and responsibility.
One way 'death' can be unique is if it has rules specific to the fanfiction's universe. For instance, instead of being permanent, death could be a reversible state under certain conditions, like if a character has a powerful enough quirk or if they fulfill a particular quest. This would completely change the way characters approach dangerous situations.
Give Tomura a new power or ability that is unique to your fanfiction. This will set your story apart from others. For example, he could have the ability to control time for a short period.
One great 'My Hero Academia' crossover fanfiction is the one where they cross over with 'One Piece'. It combines the unique powers of the 'My Hero Academia' world with the adventurous and diverse world of 'One Piece'. The characters interact in really interesting ways, like Midoriya being amazed by Luffy's Devil Fruit powers and Luffy being intrigued by the concept of Quirks.
One idea could be that Kakashi is somehow transported to the My Hero Academia world. He could become a teacher at UA, using his ninja skills and wisdom to train the students in new and unique ways. His Sharingan would be a very interesting power in the MHA universe.
Begin by choosing the crossover concept carefully. Let's say you choose a crossover with the DC universe. Consider the personalities of the characters from both My Hero Academia and DC. Then, outline your story. You could start with a character from My Hero Academia accidentally ending up in the DC universe. As you write, make sure to keep the essence of both universes intact. Describe the new settings and how the characters react to them in detail.
To start a My Hero Academia crossover fanfiction, begin by brainstorming unique scenarios. Say you're crossing over with the DC universe. Picture how Superman's powers would compare to All Might's. Then, outline your story. Include details like how the characters from both universes will meet. You can start with a strong hook, like a mysterious event that brings them together. Also, do some research on both universes to make the crossover believable. Write down character profiles for the main characters from both worlds so you can stay true to their personalities.
First, decide on the concept or plot. It could be something like a new villain entering the scene or a different take on a character's development. Then, create an outline. This doesn't have to be super detailed but should cover the main events in your story.
You can also combine different concepts. Maybe Izuku has a quirk that is a mix of telekinesis and heat generation. He could move objects with his mind while also heating them up, creating a powerful offensive and defensive ability. This would require him to train hard to control both aspects of his quirk effectively.
In a fanfiction scenario, the Hulk might be a result of a secret experiment by the League of Villains to create an ultimate weapon. But instead of being fully controllable, he breaks free and becomes a wild card in the power dynamics of the My Hero Academia world. His presence would disrupt the existing balance between heroes and villains as everyone tries to either control or destroy him.