Ron could be another main character. He might be hesitant or skeptical about the Lady of the Lake at first. And of course, there could be new characters created specifically for the fanfiction. Maybe a young wizard or witch who has a special bond with the Lady of the Lake from the start and guides the others in understanding her role.
One interesting aspect could be new magical creatures introduced in such fanfictions. Maybe there are unique interpretations of the Lady of the Lake within the Harry Potter universe. For example, she could have a special connection to the Forbidden Forest and its secrets.
The Dark Lady in Harry Potter fanfiction could be a variety of things. It could be a long - lost relative of a major character who has turned to the dark side. For example, she could be a distant cousin of the Malfoys who has her own agenda in the wizarding world that involves dark magic. She might also be an entirely new creation who fills a role that wasn't explored much in the original series, such as a female dark wizard who challenges Harry and his friends in ways different from Voldemort.
The Dark Lady could be an ancient witch who was once a powerful figure but was banished for her dark practices. Maybe she was a rival of one of the great wizards in the past and now she's back to seek revenge.
It could be an original character created by the fanfiction writer. A witch who has been in the shadows for a long time, biding her time to rise to power.
Another theme is relationships. A female Harry might have different dynamics in her friendships with Hermione and Ron. There could also be new romantic interests and how she would handle love in the context of the dangerous wizarding world. Additionally, self - discovery is a big theme. As a lady, she has to figure out her own identity in a world that has different expectations for women.
Well, in many 'Harry Potter and the Dark Lady' fanfictions, the plot often revolves around a new character, the Dark Lady. She could be an ancient evil that has been dormant for centuries and now resurfaces in the wizarding world. This might lead to Harry and his friends having to face new and unexpected challenges that are different from what they faced with Voldemort. Maybe she has her own dark magic and a group of followers who are causing chaos in Hogwarts and the wider wizarding community.
One great 'Harry Potter Grey Lady Fanfiction' is 'The Grey Lady's Secret'. It delves into the backstory of the Grey Lady in Hogwarts. It shows her relationship with other ghosts and how she might have interacted with students in a more in - depth way than what's shown in the original books.
Another possibility is a story where a spell goes wrong in the Harry Potter world and opens a portal to Asgard. Harry and his friends end up in Asgard and meet Lady Sif. They form an alliance to stop an evil wizard who has also found his way to Asgard and is trying to steal Asgardian magic for his own dark purposes. Lady Sif could teach them some Asgardian magic while they introduce her to things like the Marauder's Map.
Yes, there are some out there. You can start by looking on fanfiction websites like Archive of Our Own. Just search for 'Harry Potter and Lady Sif' and you'll likely find a variety of stories, some might be about them teaming up in a magical adventure, or perhaps a crossover story where the worlds of Harry Potter and Thor (where Lady Sif is from) collide in an interesting way.