You could write an Inception fanfic that focuses on the backstories of the existing characters. For example, explore how Cobb met and trained with his mentor. Or perhaps a story about Arthur's first experience in shared dreaming. It would give more depth to the characters we already know and love from the movie.
The relationships Arthur has with other characters in Inception also make the fanfics interesting. Writers can explore his friendships, rivalries, and how he works with others in different scenarios. There could be a fanfic where Arthur has to team up with someone he doesn't trust at first to complete a very difficult dream - heist, and seeing how that relationship develops is fascinating.
Well, in '1984 fanfic', one interesting idea could be exploring different endings. Maybe the main character manages to overthrow the totalitarian regime in a way not shown in the original. Another could be delving deeper into the relationships between characters that were only hinted at in '1984'. For example, the relationship between Winston and Julia could be explored further, like what if they had a chance to start a real family in a post - Big Brother world.
A kyman fanfic could explore the idea of them getting lost in a mysterious forest during a camping trip. As they try to find their way out, they face various challenges that make them see each other in a new light. Or perhaps a story where they both enter a video game world and have to team up to defeat the final boss. In this world, their usual animosity is put aside as they focus on the game objective.
One idea could be to explore an alternate timeline where Ichigo never became a Soul Reaper. Maybe he lives a normal life, but strange spiritual events still occur around him, drawing him into the world of the Hollows and Soul Reapers in a different way. Another idea is to focus on a side character, like Uryu, and tell a story from his perspective during a major arc that we didn't see much of in the original series. For example, his experiences during the Arrancar arc when he was off on his own missions.
One idea could be a fanfic that focuses on Elsa's further exploration of her powers. Maybe she discovers a new aspect of her magic in a far - off land. Another could be a story about Anna and Kristoff's adventures during their honeymoon. They could encounter new magical creatures. And a third idea is a fanfic that delves into the backstory of the Northuldra people, showing more of their culture and history before the events of Frozen 2.
You could create a fanfic where the characters go on a road trip across the country. They'd encounter different cultures and situations, which would be a great way to show their growth and how they interact with the outside world. It could also be funny to see how they deal with things outside of their familiar neighborhood.
A really cool idea for a 'the incredibles fanfic' would be to have the Incredibles travel to a different dimension. In this new dimension, the rules of superpowers are different, and they have to adapt quickly. They could meet alternate versions of themselves or new allies and enemies. This would open up a whole new world of possibilities for the story.
One idea could be to explore the backstories of the minor characters in more detail. For example, the character who only appears briefly in the original but has a really interesting look or a single line that makes you wonder about their past.
One idea could be a time - travel fanfic where Naruto or Sasuke go back in time and try to change certain events. This would allow for a lot of creative storytelling as they interact with their younger selves and try to prevent future tragedies.
For an aquaria fanfic, consider a story where a young child's love for their small aquarium grows into a magical journey. The fish in the aquarium start to show signs of intelligence and the child begins to understand them. As the story progresses, the fish lead the child on an adventure through the waters of their imagination. They encounter different sea - themed characters and learn about the importance of protecting the ocean. This could also include elements of how the child's care for the aquarium is like taking care of a small part of the ocean.