Cooperation is another theme. Some fanfictions explore the idea of humans and Godzilla working together. This could be for mutual protection, like in a world where there are other threats that are bigger than both of them. It makes for an interesting dynamic as they have to overcome their differences, with Godzilla being a giant monster and humans being, well, humans.
One common theme is survival. Since Godzilla is such a powerful and often dangerous creature, the humans in these fanfictions are usually focused on just staying alive in his presence. For example, in many stories, they have to find ways to avoid being crushed or caught in the crossfire of Godzilla's battles.
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.
One common theme is the battle between colossal forces. You have Godzilla, a huge and powerful creature, and the Jaegers from Pacific Rim, which are also massive and strong. So, there's often a lot of epic fight scenes.
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.
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.
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 self - discovery. The human kid often enters the Lion King world not fully understanding themselves, but through their adventures, they learn about their own strengths and weaknesses. For example, facing a dangerous situation might make them realize they're braver than they thought.
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.
One popular 'human godzilla crossover fanfiction' is 'Godzilla's New Ally'. In this story, a scientist discovers a way to communicate with Godzilla and they team up to fight a new, even more menacing monster. It has great action scenes and an interesting take on how humans and Godzilla could interact.