It could mean that Bill, perhaps a character or a person in the context related to the Harry Potter fandom, guards or looks out for Harry Potter fanfiction. Maybe he tries to prevent it from being misused, like protecting it from being plagiarized or from getting baseless negative criticism.
One great 'Bill Protective of Hermione' fanfiction is 'Bill's Guard'. In this story, Bill is constantly looking out for Hermione during a dangerous time at Hogwarts. He uses his experience as a curse - breaker to keep her safe from dark wizards lurking around. It has some really nice character interactions and shows Bill's loyalty towards Hermione.
The appeal of Bill being protective of Hermione in fanfiction lies in the contrast of their characters. Bill is a worldly, experienced wizard and Hermione is this brilliant but sometimes naive bookworm. It creates a dynamic where Bill's experience can safeguard Hermione's inquisitive nature.
In some versions, Neville could also be one of Harry's protective mates. Neville, who grows in courage throughout the series, would be willing to stand up against any threat to Harry. And Luna, with her unique perspective and magical abilities, might also be part of Harry's protective group.
Maybe Blaise sees something special in Harry. In fanfiction, it could be that Blaise admires Harry's courage or his unique abilities. He might feel a sense of kinship with Harry despite their differences.
At first, it might be a bit awkward as they come from different generations in the wizarding world. But as they spend more time together, they start to understand each other's strengths and weaknesses. Harry admires Bill's knowledge of magic and his courage, while Bill is drawn to Harry's selfless nature.
Well, it could be that in the fanfiction's plot, Harry has some special qualities or is in a dangerous situation. Edward, being a character with his own set of values, decides to be protective. For example, if Harry has some sort of power that others might want to misuse, Edward would step in to safeguard him. It might also be related to their shared experiences or a bond that has developed between them over the course of the story.