The length of the fanfiction can also play a role. Longer and more complex fanfictions that require a big time investment to read might have been forgotten. People might have started them but not finished, and as new, shorter, and more accessible fanfictions became available, these longer ones got pushed aside. Additionally, if the writing style was very different from what was popular at the time, it could have been overlooked. For example, if it was written in a very experimental or archaic style, it might not have gained a wide readership and thus became forgotten.
Perhaps it could be a character who was previously thought to be a Muggle - born but actually has a hidden wizarding heritage. In the fanfiction world, they could discover that they are the heir to a powerful wizarding legacy through some strange events or revelations. This would completely change their perception of themselves and their place in the wizarding world.
One interesting 'Harry Potter forgotten fanfiction' could be about the adventures of minor characters that were overlooked in the original series. For example, a story focusing on the house - elves and their secret lives in Hogwarts. They could have their own little quests and relationships that we didn't get to see in the books.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own (AO3). These platforms have a vast collection of fan - created works, and you can use the search function to specifically look for 'Harry Potter forgotten fanfiction'. Just type in relevant keywords like 'forgotten' along with 'Harry Potter' and browse through the results.
In some Harry Potter fanfictions, the idea of a forgotten brother can add a whole new layer of mystery. It could be that this forgotten brother was hidden away for his own protection, perhaps from Voldemort. Maybe he has some unique magical abilities that no one else in the family has. This forgotten brother might also have a different relationship with the magical world compared to Harry, like being more in tune with the dark arts or having a special connection to certain magical creatures.
There might be some new characters created specifically for this fanfiction. They could be people or creatures that Harry meets during his time of being forgotten and they play important roles in his journey. For example, an old wizard living in seclusion who takes Harry under his wing and teaches him things he wouldn't have learned otherwise.
Obviously, Harry Potter is a main character. He's the one who has been forgotten by his parents. His friends Hermione and Ron might also play important roles as they usually do in helping Harry through his difficulties.
One possible role is that of a savior. Just as Harry was seen as the one to defeat Voldemort, the forgotten brother could have an even greater destiny. He might be the one to finally bring true peace to the wizarding world. Another role could be as a villain. Maybe he was left out and forgotten for so long that he harbors a deep resentment towards his family and the wizarding world in general. He could then seek revenge on those who ignored his existence.
One interesting plot could be Harry finding new, unexpected allies outside of Hogwarts who help him build a new sense of self - worth when his family has forgotten him. For example, he might meet some magical creatures that understand his pain and offer him a place to belong.