No. Harry Potter is a unique and original story created by J.K. Rowling. It has its own independent world - building, characters, and plotlines that are distinct from fanfiction. Fanfiction is typically based on existing works by fans, while Harry Potter is a fully - fledged, professionally - written series.
One possible fanfic could be about Madam Pomfrey's early days at Hogwarts. Maybe she had to deal with some very difficult magical maladies that no one else knew how to handle. She could have been a young and inexperienced healer then, but her determination and natural talent for healing gradually made her the respected figure she is in the series.
In Harry Potter fanfiction, Madam Hooch and lemon could potentially be part of a really interesting plot. Maybe a potion recipe gone wrong in her class involves a lemon, and it creates some sort of chaos among the students. For example, the lemon could react with a flying broom charm and make the brooms go haywire.
The vastness of the Harry Potter world. It has so many elements like Hogwarts, Quidditch, the Ministry of Magic, etc. that are not related to the Lestranges at all. It's about Harry's journey, not just some side - story related to the Lestranges.
A 'harry potter x oc lestrange fanfic' might focus on the contrast between the established world of Harry Potter and the new elements brought by the OC. For example, if the OC is a student at Hogwarts, how do they deal with the secrets and politics within the school that are often influenced by the Lestrange family's history. It could also show how the OC might change the fate of certain characters or events due to their unique perspective or abilities.
One good place to start looking for such fanfics is Archive of Our Own (AO3). It has a vast collection of Harry Potter fanfics, and you can easily search for ones related to 'oc lestrange'. You might find some gems there.
Rabastan Lestrange is a rather dark and complex character in the Harry Potter universe. In fanfic, he can be explored in various ways. He was a Death Eater, which means his actions were often cruel and in line with Voldemort's evil plans. Some fanfics might focus on his time in Azkaban and how that changed him, or they could explore his relationships within the Death Eater ranks, such as with his brother Rodolphus. His loyalty to Voldemort is also a key aspect that could be delved into in fanfic.
He's often portrayed as a menacing figure. Since he was a Death Eater, he's usually shown as being loyal to Voldemort's cause. In many fanfics, he's involved in dark magic and evil schemes.
The idea of Harry Potter being the son of Rabastan Lestrange in fanfiction is quite wild. It would likely involve a lot of changes to the original plot. For example, his time at Hogwarts could be full of challenges as he tries to fit in while also dealing with the stigma of his new family. His skills in magic might develop in a different way too. He could have a natural inclination towards the Dark Arts, which he would have to struggle with. And the way the story would handle his relationship with Voldemort would be very different, perhaps even more complex.
Voldemort is often paired with Bellatrix in fanfiction. Their relationship in the original series was one of master and servant, but in fanfiction, it can be explored in more complex and romantic ways. Another character often paired with her is Narcissa. Their sisterly bond can be a central focus, or it can be twisted into something more sinister or complex in fan - created stories. Also, sometimes Sirius Black is paired with her in alternate universe stories, given their family connection and the contrast in their loyalties.