Another common theme is the protection of Earth. Both Superman and the Avengers are all about saving the world. Fanfictions often center around a huge threat to Earth that requires both Superman and the Avengers to combine their strengths. This could be an alien invasion much larger than what either group has faced alone, and seeing how they strategize and fight together is always exciting.
One popular theme is alternate universes. Writers like to explore what would happen if certain events in the MCU went differently, like if Iron Man didn't build the first Iron Man suit. It gives a whole new perspective on the characters.
Another theme is the exploration of their Kryptonian heritage. Writers may delve into the lost culture of Krypton, how it affects the characters' identities, and how they use their Kryptonian abilities in new and interesting ways. For instance, they might discover new powers or ways to use their existing powers based on ancient Kryptonian knowledge.
One possible plot could be that Superman finds himself in the Marvel universe due to some sort of interdimensional rift. The Avengers initially see him as a threat. But then they realize he's there to help against a common enemy like Thanos. Superman's powers would be a huge asset, and his sense of justice would align with the Avengers' mission.
Another interesting piece is 'When the Man of Steel Joins the Avengers'. In this fanfiction, the writer explores how Superman's moral code affects the Avengers' decision - making processes. It also has some great character development for both Superman and the Avengers members.
Superman and Captain America would likely respect each other a great deal. They both have strong moral compasses. Superman might be impressed by Cap's leadership skills. Iron Man, on the other hand, would probably be curious about Superman's powers and how they work. Thor might see Superman as a worthy ally, like another powerful being from a different world.
A common theme is She - Hulk's struggle to balance her normal life as Jennifer Walters and her superhero identity. For example, in many fanfictions, she has to deal with legal cases during the day and then rush off to save the world at night.
It's also popular because it allows fans to create their own versions of Superman's story. They can introduce new villains, new relationships, or even change the outcome of certain events in the movie. For example, some fanfictions might explore what would have happened if Superman had made different choices during his battles. This creative freedom is very appealing to fans.
Well, surely the original Avengers like Iron Man, Captain America, Thor etc. would be main characters. Their characteristics and abilities would likely be adapted to fit the 'steel' theme in some way.
Another theme is the power of friendship. The 'good man' character forms strong bonds with the Avengers. These relationships are what help him face various challenges. For instance, his friendship with Captain America might inspire him to be more selfless and brave in battles.
Character development is also a big theme. Fans might write about how a character from one universe would change or grow if they were exposed to the other universe. For instance, how Tony Stark would interact with Sherlock and how that might influence his own character arc.