One common theme is female empowerment. These fanfics often show the female monsters being strong, independent, and capable of handling difficult situations on their own. For example, they might be the ones to solve a big problem in the Underground.
Another good one is 'Undertale: All - Female Monsters' Adventures'. In this fanfic, the female monsters go on a journey together. They face different obstacles and enemies while exploring new parts of the Underground. It's full of action and also has some really heart - warming moments as they support each other throughout their adventures.