Yes, there are quite a few. Some explore how a sister would change the dynamic of Harry's family and his adventures at Hogwarts. For example, she might be an additional source of support for Harry or have her own unique magical abilities that come into play during the fight against Voldemort.
Well, often the sister is used to explore family relationships more deeply. Maybe she has memories of their parents that Harry doesn't, which helps him understand his family history better. Also, a lot of these fanfictions have the sister being sorted into Gryffindor like Harry, and they become a duo that everyone at Hogwarts looks up to. They face challenges together, like dealing with bullies or difficult professors, and their bond grows stronger through these experiences.
In certain versions of such fanfictions, the big sister could be a part of some secret plan against Voldemort that Harry is initially unaware of. She might be training in some ancient magic that later helps Harry in his fight. For example, she could be learning about a powerful spell that can break through Voldemort's defenses.
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.
The plot might revolve around the older sister being a part of a prophecy too. Just like Harry, she has a special destiny. But instead of being in the spotlight like Harry, she works behind the scenes to ensure Harry's success in the fight against Voldemort. She could be the one who finds out about Horcruxes first and guides Harry in that direction, all while dealing with her own challenges at Hogwarts, like trying to keep her identity as Harry's sister a secret from the wrong people.
Sister Lemon is a fictional character created specifically for this fanfiction. She doesn't exist in the original Harry Potter series. She's likely a character designed by the fanfiction writer to add a new element to the well - known wizarding world of Harry Potter.
There could be various storylines involving Heather as an older sister in Harry Potter fanfiction. Maybe she's a Gryffindor like Harry and helps him out in his adventures, or she could be a Slytherin with her own complex motives.
In such fanfiction, it could lead to a whole new dynamic within the wizarding world. Maybe she'd have her own unique powers or play a crucial role in Harry's adventures.
In some fanfictions, it could be an original character created by the author. Maybe a witch who was the result of an affair that his father had before he married his mother. However, this is completely against the canon of the original books, but in the world of fanfiction, anything is possible.