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.
If Harry Potter had a sister in fanfiction, it could completely shift the dynamic of his relationships. She might be more popular or less so than Harry, which would affect how people interact with them both. Also, she could be the target of Voldemort as well, or perhaps Voldemort would try to use her against Harry. This would add another layer of danger and complexity to the story. And if she was friends with different characters, like being really close to Hermione before Harry was, it would change the way the trio formed.
Perhaps she would have different magical abilities compared to Harry. While Harry is known for his connection to the Patronus charm and his ability to speak Parseltongue, she could be a natural at things like divination or arithmancy. This would make their dynamic interesting as they would each bring different skills to the table when facing the various threats in the wizarding world.
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.
Her personality might be the opposite of Harry's in some ways. While Harry is often quiet and introspective, she could be outgoing and talkative. She might be the one who easily makes friends and is popular among the students at Hogwarts. However, she could also have a deep sense of loyalty, just like Harry, and would do anything to protect her friends and family. And she could be really creative, coming up with unique solutions to problems that Harry might not have thought of.
If Harry Potter had a twin sister in fanfiction, it would likely make the story more complex. She could have been sorted into a different house, like Gryffindor or Ravenclaw. This would have given her a different set of friends and experiences. Her relationship with other characters would also be different. For instance, she might have had a closer bond with Hermione or Ron in a unique way. And in battles, she could have used her own unique skills, perhaps being more stealthy or having a special talent for defensive magic.
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.
Her personality might be a contrast to Harry's. While Harry was often impulsive, she could be more cautious. She might be more of a thinker, using her intelligence to analyze situations. However, she would still have that Gryffindor courage deep down. In social situations, she could be more outgoing than Harry, making friends more easily. And she might have a special interest in magical creatures, spending her free time in the Forbidden Forest studying them.
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.
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.