A lot of the fanfictions might explore the idea of redemption for Edward Nygma. Eliza could be the character who helps him on this journey. There could also be themes of adventure, where they go on quests together. And of course, there's the theme of intelligence. Both characters are intelligent, and the fanfictions might show them using their smarts in different situations, like solving complex problems or outwitting their enemies.
You can try searching on fanfiction websites like Archive of Our Own (AO3). Just type in 'Edward Nygma Eliza' in the search bar, and it should show you a list of relevant fanfictions. There might also be some on FanFiction.net, but AO3 usually has a wider variety.
It's inappropriate. Fanfiction should be a creative way to expand on the story, characters and concepts of the original work in a positive and respectful way. 'Gotham sex fanfiction' goes against this by introducing sexual content which has no place in the Gotham narrative and can potentially damage the reputation of the Gotham franchise.
It could be amazing. Imagine Clark Kent from Smallville finding himself in the dark and gritty Gotham. He might use his powers to help Batman clean up the city in a different way. Their different moral compasses could lead to some interesting interactions, like Clark's more idealistic view clashing with Batman's darker pragmatism.
One great aspect of Gotham Mad Hatter OC fanfiction is the opportunity to expand the already dark and twisted world of Gotham. An original character (OC) can bring new perspectives to the Mad Hatter's story. For example, an OC could be a detective who has a personal vendetta against the Mad Hatter and tries to understand his mind -games from a psychological perspective. This can add depth to the existing lore and create interesting plot twists.
The Joker could be the kidnapper. He's always up to some crazy scheme and kidnapping Bruce would be right up his alley. He might want to torture Bruce both physically and mentally, just for his own twisted amusement.
One of the most interesting aspects of 'Batman Gotham by Gaslight' fanfiction is the unique setting. The steampunk Gotham City creates a whole new atmosphere for Batman's adventures. It's a place where old - world charm meets modern - day crime - fighting concepts.