Sure, Rachel Dawes is part of the Batman comic world. Her presence adds depth and complexity to the overall narrative of Batman's adventures in Gotham.
One common theme is the exploration of their relationship in different universes. For example, in some fanfics, they might be in a world where Gotham is more peaceful, and they can focus more on their personal relationship without the constant threat of villains.
You can start by looking on popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - created works, and you're likely to find several 'Batman and Rachel' fanfictions there. Just use the search function and type in 'Batman and Rachel' and you'll get a list of relevant stories.
There might be a fanfiction where Batman has to save Rachel from a new super - villain in Gotham. This could explore their relationship deeper as Batman realizes how much Rachel means to him while fighting to keep her safe. Maybe in this story, Rachel also plays a key role in helping Batman understand the villain's motives better.
One interesting story could be about Bruce's internal struggle between his love for Rachel and his duties as Batman. Maybe in the fanfiction, he tries to find a way to have a normal relationship with her while still protecting Gotham.