There are many fanfiction communities out there, but it's important to note that mpreg (male pregnancy) is a very niche and often not mainstream concept. You could also try reaching out to the Hetalia fandom communities (as Russia and Prussia are from Hetalia). They might be able to point you in the direction of some relevant fanfiction, either through their own collections or by giving you better search tips.
One common theme could be the exploration of the relationship dynamics between Russia and Prussia during the pregnancy. How they support each other or deal with the challenges that come with such an unusual situation.
One popular 'russia x prussia fanfiction' might be 'The Unlikely Bond'. It delves into how their different personalities, Russia's stoicism and Prussia's pride, interact in various situations. They might start off as rivals but gradually develop a deep understanding of each other.
It's likely to have a niche popularity. Only a specific group of fans who are interested in both the relationship between Germany and Prussia and the concept of mpreg would be drawn to it.
In the 'germany x prussia mpreg fanfiction', it could potentially be a creative exploration of their relationship. The idea of mpreg in this context can be seen as a tool for fanfiction writers to play with gender norms and traditional relationship expectations. It may also incorporate elements of their historical past, like their shared heritage and how that might play into the story of a male pregnancy. For example, how their cultural values could influence their reactions to such a situation, whether it's shock, acceptance, or a complex mix of both.
A common theme is the clash of cultures. Russia has its own rich Slavic culture, while Prussia has a distinct Germanic influence. Fanfictions often explore how these two different cultures interact when the two characters are together.
Cultural exploration. Fanfics might delve into the differences and similarities between their cultures. Prussia was known for its discipline and military - centered society, while Russia has a rich tapestry of traditions, from Orthodox Christianity to its folk arts. A fanfic could explore how characters from these two cultures interact, misunderstand, and then learn from each other.
One popular 'america x prussia fanfiction' is 'The Unlikely Alliance'. It shows an interesting dynamic between the two characters, with America's brashness and Prussia's pride clashing and then gradually finding common ground. Another good one could be 'Across the Ocean'. It delves into how their different cultures and histories affect their relationship in the fanfiction world.
One great Prussia x England fanfiction is 'The Prussian and the Englishman's Adventure'. It has an interesting plot where Prussia and England are forced to team up on a diplomatic mission. They start off bickering but gradually develop an understanding and a deeper connection.
One popular 'prussia x austria fanfiction' is 'The Bonds of History' which beautifully portrays their complex relationship through various historical events. It shows how their interactions shaped the political and cultural landscapes around them.
One place to find Prussia x Liechtenstein fanfiction could be Archive of Our Own (AO3). There are often various works exploring their relationship in different settings, such as historical AUs or modern-day meet - cutes. Just search for the relevant tags.