Common themes in 'Hetalia Black Dog Harry Potter' fanfics can be quite diverse. Identity is one. The Hetalia characters already have their national identities, and in the Harry Potter world, there are identities like Muggle - born or Pure - blood. How these identities interact can be a theme. Another theme could be loyalty. Characters from both universes might have to choose between their loyalties to their home countries (in Hetalia) and their newfound friends or causes in the Harry Potter world. There's also the theme of discovery, as the Hetalia characters discover the magical world and all its wonders and dangers.
There are quite a few fanfics out there. One way to find them is to check on fanfiction.net or Archive of Our Own (AO3). Just search for 'Hetalia Black Dog Harry Potter' on their search bars and you'll likely get a list of relevant fanfics.
One common theme is her loyalty to Voldemort. Many fanfics explore how deep - rooted her loyalty is and what might have led to it. Another theme is her family background, especially her connection to the Black family. Her relationship with Narcissa and Sirius is often a point of focus. And of course, her role as a Death Eater, which includes her actions during the wizarding wars.
One common theme is cultural exchange. Since Hetalia is about different nations, when combined with Harry Potter, it often shows how the different cultures of the Hetalia characters interact with the magical culture of the Potterverse. For example, how they react to magic spells compared to their own 'powers' in Hetalia.
One common theme is the clash and then the eventual harmony of different cultures. The magical culture of Harry Potter and the cultural aspects of Russia in Hetalia often start off at odds but then find a way to coexist. For example, different views on magic usage or social hierarchies.
Well, the theme of destiny is quite common. Fanfics often play with the idea that Orion Black and Harry Potter are somehow fated to cross paths and have a relationship. This could be related to prophecies or some greater magical plan. Another recurring theme is the clash of different generations. Orion comes from an older era of the wizarding world, and Harry from a more modern one. Their relationship can highlight the differences and similarities between the two generations, including their views on magic, society, and family.
Another common theme is family. The Black family has a complex history and structure. Fanfics often delve into how Harry might fit into that family dynamic. Maybe he becomes a sort of catalyst for change within the Black family, or he has to navigate the often - dark family secrets. Some fanfics also explore how Orion Black's relationship with Harry could affect his relationship with other family members, like Sirius or Bellatrix.
One common theme is redemption. Since the Black family has a rather dark history in the 'Harry Potter' universe, many fanfics with partial endings focus on how the family members can redeem themselves. For example, they might show Sirius Black's attempts to break free from the family's dark legacy.
One common theme is friendship. Just like in the original Harry Potter series, the dog often forms strong bonds with the characters in the story.
One common theme is cultural exchange. Since it's Ameripan, there's often a focus on how the American and Japanese cultures interact within the Hetalia world. Another theme is friendship or relationship building. The 'Curl' might be something that ties the characters together in this regard. For example, it could be a shared trait or a memory related to the curl.
One common theme is cultural exchange. Since America and New Zealand have distinct cultures, fanfics often explore how they share and learn from each other. For example, a fanfic might show an American character trying New Zealand's famous pavlova and being amazed by it.