Yes, there are. You can start by looking on platforms like Fanfiction.net or Archive of Our Own. Some stories might focus on Narcissa's journey in becoming an Animagus, exploring the magic and secrecy involved. Others could tie it in with her relationships within the Black family or the wider wizarding world.
A snake could be a possible form. Given the association of the Black family with Slytherin, and snakes being a symbol of Slytherin, it would make sense for her Animagus form to be a snake. It would also tie in with the cunning and secretive nature often associated with both Narcissa and snakes.
I'm not entirely sure if there is a specific fanfiction with 'Harry is a black lion animagus' but it's a very interesting concept. The Harry Potter fandom is vast and diverse. Some fanfictions are really well - hidden. You might have to dig deep into the archives of fanfiction websites or even contact some of the more dedicated Harry Potter fanfiction writers to see if they are aware of such a work.
Bellatrix Lestrange could be a great addition. Her extreme loyalty to Voldemort and her relationship with Narcissa as sisters, and her hatred for Sirius as a blood traitor, would add a lot of tension to the story.
A third common theme is adventure. His Animagus form allows him to go on adventures that he couldn't as a human. He can explore places, spy on enemies, or rescue friends more easily. Fanfictions often take advantage of this aspect and create exciting adventure - filled plots around Sirius's Animagus abilities.
A fanfiction could explore the idea of a hybrid world where the magic of Harry Potter and the technology and culture of Wakanda in Black Panther co - exist. Animagus forms could play a crucial role. For example, some characters from the Black Panther universe might learn the Animagus transformation from Harry Potter or his friends. This could lead to new forms of magic - technology hybrids. Maybe a Wakandan Animagus could use their animal form to access hidden areas of the magical world that are otherwise inaccessible, creating a whole new set of stories and challenges.
A plot could revolve around Narcissa and Sirius in their Hogwarts days. They could be involved in a mystery within the school, like a series of strange disappearances of students. Since they are both from the Black family, they might have some inside knowledge that helps them solve the mystery, and in the process, form an unexpected bond.
Narcissa Black is a character full of contradictions. Coming from a family with a strong stance on pure - blood supremacy, she marries into another powerful pure - blood family, the Malfoys. Throughout the 'Harry Potter' series, we see her loyalty being tested. While she is initially associated with the Dark side through her family and husband, her love for her son makes her take actions that could be considered against the Dark Lord's wishes. Her character is a great example of how family and love can influence a person's actions even in a world filled with magic and danger.
In the 'Harry Potter' story, Narcissa Black Malfoy was part of the complex web of the wizarding world. Her family's beliefs in pure - blood supremacy were a significant part of her background. However, as the story progressed, we saw her maternal instincts override some of those more rigid family values. Her relationship with other characters like Bellatrix Lestrange (her sister) also added depth to her character and the overall story.
One common theme is the exploration of family loyalty. Both James and Narcissa come from prominent wizarding families, and their actions are often influenced by their family ties. Another theme is the contrast between the Gryffindor and Slytherin values. James is a Gryffindor, known for courage, while Narcissa is a Slytherin, associated with cunning. Fanfictions often play with how these different values interact when they are together.