You can try searching on fanfiction websites like Archive of Our Own (AO3). They usually have a wide range of fan - created works, including Batman x Copperhead fanfics. Just use the search bar and type in the relevant keywords.
A Batman x Atwoman fanfic could also be set in an alternate universe. In this universe, Gotham and Atwoman's city are somehow connected. Batman discovers a link between some strange occurrences in Gotham and events in Atwoman's city. He travels there to investigate and meets Atwoman. Together, they embark on a journey to uncover the mystery behind this connection. Along the way, they encounter different cultures and villains specific to her city, which makes for an interesting dynamic as they try to combine their skills to solve the problem.
A Batman x Atwoman fanfic could also focus on the emotional side of their relationship. Imagine Atwoman has a personal vendetta against a particular villain. Batman initially doesn't understand why she is so obsessed. But as he gets to know her story, he realizes that it's similar to his own quest for justice. This understanding brings them closer. They start to share their feelings and fears, and this newfound emotional bond helps them become even stronger allies when facing the challenges in their cities, whether it's fighting gangs or stopping mad scientists.
Another interesting one is 'Harley's Redemption'. This fanfic focuses on Harley's journey towards redemption with Batman's unexpected support. It delves deep into Harley's character, exploring her past traumas and how she tries to overcome them while forging a new relationship with Batman. It's quite a long and engaging read with some great character development.
One possible fanfic could be about a young boy who idolizes Batman but then discovers the allure of the Red X character. He might start to create his own version of a hero who combines the mystery of Red X with the justice - seeking of Batman. For example, in his daydreams, he imagines himself using Red X's gadgets to outwit villains in Gotham City, while still adhering to Batman's moral code.
It could be about an unexpected alliance. Maybe Batman and Copperhead are forced to team up against a common enemy in Gotham. This could lead to some interesting character interactions as they have very different moral compasses.
A common theme is the passing of the torch. Nightwing was once Robin, and now he's his own hero. Fanfics often show how Batman is dealing with Nightwing becoming more independent. Another theme is the emotional bond between them. They've been through a lot together, and this shows in how they interact in the fanfics, whether it's in times of crisis or just in their everyday crime - fighting.
The settings are also interesting. You have the bright, shiny Metropolis of Superman and the dark, gritty Gotham of Batman. Fanfic often plays with how these two very different environments can affect their relationship and their joint missions. For example, a story might have Superman struggling to adapt to Gotham's underbelly while Batman has to deal with the more public and idealistic world of Metropolis.
One great 'batman x nightwing fanfic' is 'The Bond Beyond the Cape'. It delves deep into their complex relationship, showing how Nightwing's growth from Robin is influenced by Batman. Another good one could be 'Shadows and Wings', which focuses on their teamwork during a particularly tough time in Gotham.
A Harley Quinn x Batman fanfic can be really interesting. It often explores the complex relationship between the two characters. Harley, with her wild and unpredictable nature, and Batman, the brooding and justice - seeking vigilante. Writers might create scenarios where Harley tries to break free from her toxic relationship with the Joker and finds an unexpected connection with Batman. It could involve Harley helping Batman in his fight against crime in Gotham, while also dealing with her own internal struggles.