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.
Well, in some fanfictions, Charlie might use his dragon - handling skills to protect Harry. For example, he could train dragons to guard Harry or use his knowledge of magical creatures to fend off threats that are related to dark magic and its associated beasts.
In some fanfictions, it could be through powerful magic spells that he discovers or is taught. Maybe he stumbles upon an ancient spell in the restricted section of the library that allows him to summon a family member. Another possibility is that he unknowingly activates some kind of magical artifact that has the power to bring a sister into his life.
He might use magic to make things easier. For instance, he could use spells to cook food and clean up while taking care of his sister. Also, he'd probably rely on his friends a lot. Hermione could help with her studies, and Ron could be there for some comic relief and support.
Well, in the context of fanfiction, 'harry potter protects hogwarts' might refer to a specific plot device. Since Hogwarts is a central and beloved place in the Harry Potter universe, it's common for fanfiction writers to create scenarios where Harry, being the hero, steps up to safeguard it. It could be from an invasion of Death Eaters that the original series didn't cover, or some new magical menace. Fanfiction often explores different 'what - if' situations, and this could be one of them where Harry's role as protector of Hogwarts is emphasized.
Well, perhaps he uses his magic skills. He could cast protective spells around the Starks' territory, like a powerful Fidelius Charm to keep their location secret from their enemies.
In the original series, Harry is an only child, so the very concept of a sister is a huge deviation. This changes the family dynamics completely. Instead of just having the Dursleys as his only family situation outside of Hogwarts, now there is this sister factor.
He might start with the basics at home. Since he has his own experiences at Hogwarts, he can teach her things like the levitation charm. He could use simple objects around the house to demonstrate magic.
Well, it could be that Dumbledore, in some fanfic versions, figures it out first and then reveals it to Harry. Dumbledore is often portrayed as having a deep understanding of magic. He might have noticed some strange magical patterns or behaviors related to Harry that led him to suspect and then confirm that Harry was a Horcrux. And then he would tell Harry about it, which is how Harry comes to know.
Well, in some fanfictions, Cedric might use his magical skills to shield Harry from physical attacks. For example, he could cast protective spells like Protego Maxima to create a strong shield around Harry when they are in danger. Maybe in a situation where dark wizards are attacking, Cedric steps in front of Harry and uses his wand to fend off the spells aimed at Harry.