One idea could be exploring a different timeline where one of the main characters made a different choice at a crucial moment. For example, if Eddie had decided not to pursue music, how would his relationships and life have been different? Another idea is to focus on the backstory of a minor character and how they intersect with the main group. Maybe a character who only appeared briefly has a deep connection to one of the friends that could change the whole dynamic. Also, you could write a fanfiction about a special event that brings the group even closer together, like a trip they take where they face unexpected challenges and grow stronger as a result.
You could write a fanfic focusing on the friendship between the characters. Maybe a story about how Gary and Rome first became friends and all the adventures they had before the start of the show.
One idea could be that Gary and Maggie go on a road trip together. Along the way, they encounter various challenges that make them rely on each other more, deepening their bond. For example, their car could break down in a small town, and they have to work together to fix it or find a way to continue their journey. This would give them a chance to have deep conversations and realize new things about each other.
A friendship - centered fanfiction could be great. Maybe a new character enters the scene and forms an unlikely but strong bond with one of the main characters. They help each other through tough times, like dealing with the pressures of the mystery and the social drama in the Pretty Little Things world.
One idea could be that the Demogorgon from Stranger Things somehow ends up in Derry from It. The Losers' Club and the kids from Hawkins could team up to fight it. They would have to combine their different skills and knowledge of the supernatural.
One idea could be that the Losers' Club from 'It' somehow ends up in Hawkins, Indiana, during the events of 'Stranger Things'. They could team up with the kids from 'Stranger Things' to fight a new, combined threat that has elements of both the Upside Down monsters and Pennywise's terrors. For example, the Mind Flayer could merge with Pennywise in some way, creating an even more terrifying entity.
One idea could be to explore the backstories of the minor characters in the 'The Bureau of Magical Things'. For example, the shopkeepers in the magical world. Another idea is to create a new adventure where the main characters have to travel to a different dimension within the magical universe. And a third idea might be to write a fanfiction about a time before the events of the show, showing how the bureau was founded.
One idea could be a crossover where the ninjas from Naruto enter the Upside Down in Stranger Things. They use their jutsu to fight the strange creatures there. Another could be characters from Stranger Things learning chakra control in the Naruto universe. Maybe Eleven could use her powers in combination with Naruto's Rasengan.
One idea could be that Naruto characters are transported to the Upside Down in Stranger Things. They use their ninja skills to fight the strange creatures there. For example, Naruto could use his Rasengan against the Demogorgon.
You could have an OC that is a transfer student from a different town where strange things have also been happening. This OC could have some knowledge about the otherworldly events that the kids in Hawkins haven't encountered yet. Or make an OC who is a scientist's assistant, secretly helping the main characters by providing inside information from the lab. They might also be in danger because of this connection to the scientific side of the mystery.
A really cool crazy little things fanfiction might be one that changes the ending of the original. Instead of the typical conclusion, the author could create a new ending where the characters make different choices and end up in a completely different situation. This can be exciting for readers who want to see an alternative take on the story.