One great fanfiction could be 'The Pirate's Treasure'. In it, Pirate England and America go on an adventure to find a hidden treasure. It has a lot of action scenes and also some interesting character interactions. For example, their banter while on the ship is really engaging.
A political intrigue plotline could also be fascinating. Maybe there's a situation where they have to work together to solve an international crisis, but there are other countries trying to undermine their efforts. It would involve a lot of strategy and diplomatic maneuvering between the two characters, with some tense moments and perhaps a budding respect for each other's abilities.
Adventure is a theme that shows up as well. They could go on adventures together, exploring different parts of the world or even fictional realms. And of course, there's the theme of self - discovery. In these fanfictions, Fem America and Fem England often discover new aspects of themselves through their interactions with each other, whether it's their hidden talents or their true feelings.
I'm not sure of specific fanfics with this exact combination, but you can try searching on popular fanfic platforms like Archive of Our Own. There are often many Hetalia - related fanfics there. Just use the search terms 'Hetalia', 'Russia', 'female America' and 'pregnant' to narrow down your search.
Friendship is a very common theme. They often show how England and America have a bond that has developed over time, through shared history and experiences. For example, in many fanfictions, they start off with misunderstandings but gradually grow to understand and support each other.
In many 'America x New Zealand' Hetalia fanfics, a prevalent theme is the discovery of new things. New Zealand discovers the big - worldliness of America, and America discovers New Zealand's natural beauty and simplicity. Also, cooperation is a key theme. They often work together in fanfics, be it in dealing with international issues or just helping each other out in small ways. Additionally, there can be a theme of overcoming differences. Their different political stances and ways of life are things they have to navigate in these stories.
Well, you can try searching on Archive of Our Own (AO3). There are a lot of great Hetalia fics there. Just type in 'Hetalia America and Belarus' and then filter out the inappropriate ones. Some fics might focus on their political relationships in a more platonic and interesting way, exploring how their countries' interactions could be reflected in their characters.
One potential victim could be a small, weak nation - character. Since America is a powerful nation in the Hetalia universe, he might target a smaller nation that he suspects of having some sort of information or ability that he wants. Another could be a character who is an enemy spy in the fanfic's plot. America would want to kidnap them to get information. Also, it could be a character who has a valuable cultural artifact that America wants to 'protect' by taking the character who has it into custody.
The whole pirate aesthetic is appealing. The idea of sailing the high seas, looking for treasure, and the whole pirate culture with its own language, code, and fashion. When combined with the Hetalia characters of England and America, it creates a really interesting and exciting blend that attracts a lot of readers. The fanfictions can also bring in historical elements related to piracy and the relationship between England and America during that era, which adds depth to the stories.