One common theme is cultural exchange. Prussia and Hungary have different cultures, and in fanfictions, they often explore each other's traditions, like Prussia introducing Hungarian to his military strategies or Hungary showing Prussia her folk dances.
Friendship and loyalty are also common themes. Prussia and Hungary can be portrayed as friends who support each other through difficult times. In some fanfics, they might have to face challenges together, and their loyalty to each other is tested and strengthened. Also, there can be a theme of mutual respect. Given their different strengths and characteristics, they learn to respect one another in these stories.
There's also 'Prussia and Hungary: A Tale of Two Nations' which focuses on how their different cultures interact and how they gradually fall in love. It has some really cute moments like when Prussia tries to learn Hungarian dances to impress Hungary. It shows their relationship in a very heart - warming way, exploring not just the romantic aspect but also their political and cultural ties.
A common theme is the exploration of their cultural differences. Hungary has his own unique cultural traits and Prussia has hers, and in fanfiction, it's often interesting to see how these differences play out in their relationship.
One possible plot could be the reader being a bit nervous about fitting into Prussia's world, especially with the wedding in Hungary which has its own unique cultural expectations. Prussia would then comfort the reader and assure them that all that matters is their love. Another plot could be some sort of conflict arising from an unexpected guest who tries to disrupt the wedding. But Prussia and the reader would face it together and come out stronger.
One popular 'Prussia x Hungary fanfic' could be 'The Prussian-Hungarian Alliance'. It delves into their relationship in an alternate historical setting where they have to work together against a common enemy. The story is filled with great character interactions and political intrigue.
There are some fanfiction communities on Tumblr as well. Some users might share or create their own stories about male Hungary and fem Prussia. You can search for relevant tags like '#malehungaryxfemprussia' or '#hetaliafanfiction' to find these stories. However, the content might be a bit more scattered compared to AO3.
A third theme could be the relationship between the two characters. The pregnancy could either strengthen their bond or create new tensions. It could show how they rely on each other more than ever, or it could expose insecurities and differences in their relationship as they face the challenges and joys of impending parenthood.
I'm not sure if there are specific fanfics solely focused on Prussia and Hungary being pregnant. Fanfic topics can vary greatly, and while there might be some in the vast realm of fanfiction that touch on such concepts in the context of their relationship, it would require a detailed search through relevant fanfic platforms.
One idea could be a story where Hungary and Prussia are forced to work together on a diplomatic mission. Along the way, they start to understand each other's cultures better and develop a grudging respect that slowly turns into friendship and perhaps more. For example, Prussia could introduce Hungary to some of his military strategies, and Hungary could share her knowledge of local customs. This could create a unique dynamic as they both have strong personalities.