A prevalent theme is the power dynamic between them. Sometimes the male Godzilla is depicted as the stronger one, but in some fanfictions like 'The Equal Partners', they are shown as equals in terms of strength and intelligence. Also, the theme of discovery is common. For example, in 'The Discovery of a New Bond', they discover new aspects of their relationship and their own abilities as they face various challenges together. Love and loyalty also play a big part in many of these stories, especially in ones that focus on their relationship on a more emotional level.
One common theme is protection. Godzilla is often depicted as protecting baby Godzilla from various threats, be it other monsters or human interference. Another theme is growth, showing baby Godzilla's development into a more powerful creature over time.
Power is a common theme. Since Godzilla is already a powerful figure, when it's a female, it often explores how she wields that power differently. Another theme is motherhood, as mentioned before, like how she might care for offspring or be a protector in a maternal way.
Well, a frequent theme is the exploration of Godzilla Jr.'s powers. In the context of Godzilla Final Wars, the fanfiction might show how he discovers or hones his abilities. Also, the theme of family can be present, as Godzilla Jr. has a connection to the larger Godzilla family. And there could be themes of survival and heroism as he faces the many threats in the Godzilla Final Wars universe.
A common theme is the clash of two different power scales. Godzilla is a huge, destructive force, while Pokemon have their own unique powers. So, there's often a theme of how these two types of power interact. Another theme could be the idea of an outsider (Godzilla) in the Pokemon world, and how the Pokemon and trainers react to this strange and powerful being.
Since I haven't actually read such fanfiction, it's hard to say for sure. But perhaps themes could include the challenges of a pregnant kaiju, how the other monsters in the Godzilla universe react, or the idea of a new kind of monster being born.
One common theme is power. Godzilla is extremely powerful, and in the DxD universe which also has powerful characters, exploring how his power compares and interacts is a big theme.
One common theme is cooperation. Since they are both powerful creatures, seeing them work together against a common foe is often explored.
One common theme is the idea of two different species coming together. Godzilla and Mothra are very different in nature, so the fanfiction often explores how they overcome those differences. Another theme could be sacrifice, like one of them sacrificing for the other in a battle or difficult situation.
One common theme could be the idea of an unlikely pairing. Godzilla is a huge, powerful monster and Mandy could be a human or some other character. So, the contrast in their natures can lead to themes of acceptance and understanding in their relationship. Another theme might be adventure, as Godzilla is often associated with action - filled scenarios.
Common themes could include the impact on the monster ecosystem. With new life on the way, it might disrupt the balance of power among the various monsters. There could also be a theme of sacrifice. Maybe one of the parents has to make a great sacrifice to ensure the survival of the unborn. Additionally, the fanfiction might explore the concept of family in the context of these giant monsters, which is very different from the traditional human family concept.