One way Harry Potter could protect his sister in fanfiction is through his fame and influence. People in the wizarding world respect and fear Harry. He could use this to his advantage. If anyone tried to harm his sister, he could make it clear that there would be serious consequences. Also, he might have some special magical artifacts that he could use to protect her. For instance, the invisibility cloak could be used to hide her when needed. Harry's connection with powerful wizards like Dumbledore could also play a role. He could ask for help from them if the situation demanded it.
Dark wizards are a common threat. Voldemort's followers might target his sister to get to Harry. They could try to use her as a hostage or a way to lure Harry into a trap. Another threat could be magical creatures that are out of control. In some fanfictions, there might be a basilisk or a dementor loose near where his sister is. Also, there could be jealous classmates or rivals who might try to harm her out of envy for Harry's status.
Yes, it could be. Hogwarts is a very important place in the Harry Potter world, and Harry Potter is the main hero. So it makes sense that protecting Hogwarts by Harry is a popular theme.
One possible reason could be jealousy. Maybe the sister is getting more attention from their parents or at Hogwarts. For example, if she is a star student and Harry feels overshadowed.
Obviously, Harry Potter himself is a central character. His sister would be the new addition. Hermione and Ron are likely to be there as well. They are Harry's best friends in the original series and would probably play important roles in the fanfiction too. Dumbledore might also appear, as he is a very important figure in the wizarding world and could guide the sister in her magical journey.
If such fanfiction exists, it may lead to a lot of negative impacts. It can mislead some young and inexperienced readers into thinking that abnormal relationships are acceptable. Moreover, it might face legal issues in some cases as it violates ethical and moral boundaries. Also, it will be shunned by the vast majority of the legitimate Harry Potter fandom who uphold the positive values of the series.
Hermione would still be a very popular character. She could be the one to help the twin sister study and understand the more complex aspects of magic. Her logical thinking and vast knowledge of magic would be invaluable in their adventures.
Their parents' old friends could be main characters. They might come to check on Harry and his sister, bringing gifts and stories about their parents. These friends could offer guidance and protection when needed.
One common theme is redemption. Slytherins are often seen as the 'bad guys' in the original series, so protecting Harry gives them a chance at redemption. For example, they might be trying to make up for past wrongs or the actions of other Slytherins.
Ron and Hermione are likely to interact with them. Ron might be a bit more protective of the sister, while Hermione would probably study and share knowledge with her. They could all be in the Gryffindor common room, discussing spells and strategies.