Perhaps it's a character from a minor magical family that was thought to be extinct. Their heir could have powers that are a combination of ancient magic that was thought to be lost. They might have the ability to communicate with magical creatures in a way that no human has been able to do before, which would make them very powerful in the eyes of both those who want to protect magical creatures and those who want to use them for their own gain.
It could be Harry Potter himself. Since he has so many special qualities and a deep connection to Hogwarts, he might be revealed as an heir. Maybe he has some latent powers related to one of the founders that haven't been discovered yet.
In some fanfictions, it might be possible for Harry Potter to be depicted as the heir of Grindelwald. Fanfiction allows for a lot of creative interpretations. However, this goes against the original canon where there is no such indication.
In the fanfiction world, Harry might be the heir to Hogwarts if there was some sort of magical pact made generations ago. For example, perhaps one of his ancestors had a special role in the creation or protection of Hogwarts, and this role was passed down through the family. It could also be that his unique magical abilities, like his ability to resist Voldemort's attacks from a young age, are signs of a deeper connection to Hogwarts itself. This connection could be what designates him as the heir in the fanfiction's plot.
It could be a previously unknown character, like a distant relative of one of the main families in the Harry Potter series. Maybe a long - lost cousin of the Weasleys or a descendant of one of the founders of Hogwarts that has been living in hiding.
Hermione Granger could also be a possible Hogwarts heir. She is extremely intelligent and has a thirst for knowledge about Hogwarts' history and magic. Her Muggle - born status might seem to be a contradiction, but it could also be part of what makes her unique as the heir. She could bring new perspectives and use her vast knowledge to unlock secrets about the heir's role and the future of Hogwarts.
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 possible character is Draco Malfoy. In some fanfictions, he is explored as the Slytherin heir, given his family's pure - blood status and connection to the dark arts. Another could be an original character created by the fanfiction author. This character might be a long - lost descendant of Salazar Slytherin, with a mysterious past and special abilities. Sometimes, even Harry Potter himself is made the Slytherin heir in certain very creative fanfictions, which completely changes the dynamic of the story.
Another possibility is a student at Hogwarts who has always been in the background. A shy or overlooked character who suddenly discovers that they are the unknown heir. For instance, Neville Longbottom could be an interesting choice. He has shown great courage and growth throughout the series, and if he were revealed as the heir, it would give his character a whole new level of importance.