Luna might be initially cautious around Godzilla. Given her role as a princess in Equestria, she would likely try to assess if Godzilla is a threat. Godzilla, on the other hand, might be confused by the new environment. Eventually, Luna could use her magic to communicate with Godzilla, perhaps on a telepathic level. They would then start to understand each other's motives and find common ground, like protecting their respective homes from danger.
A plot could involve a group of villains from another world who want to capture both Godzilla and Luna to use their powers. They manage to transport Godzilla to Equestria. Luna, being the protector of the night, finds Godzilla and realizes that they need to escape and fight back. Along the way, they meet various other My Little Pony characters who help them in different ways. Eventually, they face the villains and with their combined strength and the help of their new friends, they defeat the villains and Godzilla returns to his own world, but not before a new friendship is formed between him and Luna.
Well, a frequent theme is adaptation. Godzilla has to adapt to the bright and friendly world of the ponies, and the ponies have to adapt to the presence of a huge, potentially dangerous monster. Friendship is also a theme, although it might be a bit of a stretch considering Godzilla's nature. But some fanfictions try to show how the ponies' friendship could influence Godzilla. And there's the theme of power. Godzilla has his own kind of power, and the ponies have their magic, and fanfictions often play with how these powers interact.
In a fanfiction, there could be a story where a pony discovers a magical artifact that can control Godzilla. At first, the pony uses it for fun, making Godzilla do small things like create waterfalls with its tail. But then, an evil force tries to steal the artifact to use Godzilla for destruction. The ponies then have to protect the artifact and convince Godzilla to help them fight the evil.
One common theme could be the anticipation and excitement in Equestria. The ponies might be looking forward to the new arrival. Another theme could be Luna's own journey during pregnancy, like dealing with physical and emotional changes. And sometimes, there might be a theme of unity as the ponies come together to support her.
There are likely some out there. You can start by checking popular fanfiction websites like FanFiction.net or Archive of Our Own. However, the concept of Luna being pregnant in fanfiction can vary greatly in terms of the storylines, from exploring new magical aspects in Equestria due to her condition to how the other ponies react to this big change in Luna's life.
Luna, with her connection to the moon and her magic related to the night. And Supernova, who could be a pony from a far - off land or even a new creation within the fanfiction world. They are likely to be at the center of the story, driving the plot forward with their actions and interactions. For example, their different personalities might clash at first, but then they learn to work together as the story progresses.
The theme of forgiveness is also quite common. Luna, being a more benevolent character, might be in a position to forgive Sombra for his past wrongdoings. This can lead to some really emotional and character - building moments in the fanfiction. Also, the theme of magic and its consequences is often explored. How their magic affects themselves and the world around them is a big part of many of these stories. For example, Sombra's dark magic might have unforeseen consequences that Luna has to deal with, or vice versa.
Growth and self - discovery also feature frequently. Both Twilight and Luna can grow as characters in fanfictions. Twilight might learn more about leadership from Luna, and Luna could discover new aspects of herself through her interactions with Twilight. This could be related to their understanding of their powers, their place in Equestria, or their relationships with other ponies.
One possible plot could be that Godzilla somehow gets transported to the world of My Little Pony. The ponies are initially terrified, but then they realize Godzilla is there because he's being chased by an even greater threat from his own world. So, the ponies, with their magic, decide to help Godzilla fight off this threat and in the process, they learn about each other's strengths and form an unlikely friendship.