Imagine a fanfiction where Captain Marvel uses her energy - based powers in a completely new way during the final battle in Avengers: Endgame. Instead of just punching and flying around, she could manipulate the energy fields in a way that disrupts Thanos's entire army. This would be a creative take on her character and her abilities.
Another fanfiction idea could be a prequel to her role in Avengers: Endgame. It could show what she was doing in the cosmos just before she received the call to return to Earth. Maybe she was facing a different threat that was related to Thanos in some way, and this backstory could add more depth to her character in the movie.
One idea could be Captain Marvel bringing back some alien tech that the Avengers have to figure out how to use. It could lead to new powers for some of the members or a new way to defend Earth.
In some 'Avengers Endgame Fix It Fanfiction', there might be a concept of time travel without the glitches that occurred in the movie. Maybe they could have a more stable time - travel device which allows them to not only reverse the snap but also fix other events that led to Thanos' victory. This could involve changing things like Loki's escape with the Tesseract in a more beneficial way for the Avengers.
A post - Avengers Endgame fanfiction could center around the psychological impact on the survivors. Like Natasha's death still haunts the team. How does Steve Rogers' decision to go back in time and live his life with Peggy affect the others? It could also be about the search for new Infinity Stones. What if there are more Stones out there? And another idea is to write about the Avengers mentoring a new team of young heroes, passing on their skills and knowledge in a post - Endgame setting.
In a rewrite fanfiction, perhaps Loki could have faked his death all along. He could then return during the events of Endgame, bringing with him an army of Asgardians he had secretly been gathering. His cunning and strategic mind could add a whole new layer to the battle plans against Thanos and his forces.
A plot could be about an alternate universe where Captain Marvel is initially distrusted by the Avengers. She has to prove herself and in the process, they all learn more about each other's powers and pasts. This could lead to some great character development and new alliances within the team.
A really cool plot idea could be that the Avengers are watching Endgame in a sort of 'alternate reality cinema' where the events in the movie start to bleed into their real world. So they have to stop the movie from fully playing out to prevent chaos in their own universe. This would involve a lot of action and strategic thinking as they try to stop things like Thanos from emerging from the screen while also trying to understand the significance of what they're seeing in the movie.
One idea could be Captain Marvel arriving just in time during the final battle in Infinity War. She could use her powers to turn the tide against Thanos. For example, she might team up with Doctor Strange to create a powerful energy shield to protect the remaining Avengers while they figure out a way to remove the Infinity Stones from Thanos' gauntlet.
One idea could be a crossover with the Doctor Who universe. The Avengers could team up with the Doctor to fight a common enemy that threatens both their universes. Maybe Thanos somehow gets access to Time Lord technology and the combined forces have to figure out how to stop him from using it to rewrite all of reality.
Perhaps a fanfiction where the Infinity Stones in the Endgame have an unexpected effect on certain anime characters. These characters start to develop new abilities or forms that are a blend of their anime selves and the power of the Stones. This could lead to a whole new dynamic in the fight against Thanos, as the Avengers have to figure out how to work with these newly - empowered anime allies.