One main theme is power dynamics. The Black Triangle consists of strong nations, and their struggle for power and influence is often explored. Another theme is loyalty, as they have to decide where their loyalties lie within the triangle. And there's also the theme of rivalry.
One popular hetalia black triangle fanfiction is 'The Unlikely Alliance'. It delves into the complex relationships within the Black Triangle. Another good one is 'Black Triangle: Shadows of the Past' which explores their historical interactions in a very interesting way. And 'Triangular Entanglement' offers a fresh take on the dynamics of the Black Triangle.
The unique character dynamics. The three characters in the black triangle trio have distinct personalities, and in fanfiction, their interactions can be explored in new and exciting ways.
Sure. You can try searching on Archive of Our Own (AO3). There are often many great works there. Just type in 'hetalia black triangle trio fanfiction' in the search bar and you'll get a list of relevant stories.
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.
Maybe the Black Butler characters are sent to the Hetalia world. Sebastian could be intrigued by the different cultures and politics of the countries. He might use his charm and skills to manipulate some of the smaller countries for his own or Ciel's gain. Grell could go wild with excitement over all the new 'pretties' he could potentially reap in this new world filled with so many different characters. And Ciel would be constantly trying to figure out how to get back to his own world while also dealing with the strange international relations in Hetalia.
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.
The 'European' aspect of these fanfics also enriches the fandom. It helps fans to better understand the different European cultures that are represented by the Hetalia characters. For example, a fanfic might describe in detail how a character's behavior is influenced by their 'national' culture in a European context. This can lead to more in - depth discussions and a greater appreciation for the Hetalia concept among fans. Moreover, the exploration of gay relationships can break some traditional relationship norms in fan works, making the fandom more inclusive.
One more interesting pairing could be Undertaker and America. Undertaker's mysterious and somewhat macabre nature against America's bold and brash attitude. America might be curious about Undertaker's strange hobbies and Undertaker could be intrigued by America's naivete and strong sense of justice. It would be fascinating to see how they interact, whether they become friends or end up at odds with each other. Also, Mey - Rin and Japan could have an interesting dynamic. Mey - Rin's clumsy but kind - hearted nature and Japan's reserved and traditional ways could lead to a unique relationship where they learn from each other.