She could have a very different relationship with Harry. Instead of being just friends, she might be more like an older sister figure, using her family knowledge to guide him. With Ron, their relationship could be more complex. Maybe there would be some jealousy from Ron as Hermione would have a more prestigious family background. And with the other members of the Black family, she would have a family bond. Some of the Black family members who were against Voldemort could be her allies in a more personal way.
Well, Hermione being James' twin sister would make her and Sirius have a tight - knit relationship. Sirius would be part of her family in a way. He'd be there for her during her Hogwarts years, and they could bond over their shared love for James. Sirius might also teach Hermione some of the more secretive and dangerous spells that the Marauders knew, and Hermione would keep Sirius in line with her logical thinking and rules - following nature, creating a balanced and loving relationship.
Her twin sister could be really outgoing. While Hermione is often seen as a bit reserved in social situations, the sister could be the life of the party. She might be more interested in Quidditch than Hermione and be a great flyer. Also, she could be more impulsive. Hermione thinks things through carefully, but the sister could be the type to jump into action without much planning.
She would have a very close relationship with them. Since she is Lily's twin, James would be her brother - in - law. She would be like Harry's aunt. They would have likely grown up together, and Hermione would have been part of the family. She would have been there during important family moments, and her relationship with James and Lily would be based on both family ties and mutual respect for each other's magical abilities.
If Hermione were Sirius's twin sister in fanfiction, it would mean a major shift in her character arc. Firstly, her appearance might be different as she would likely inherit some Black family traits. Her magical abilities could also be influenced. In the original story, Hermione was always an over - achiever, but with the Black family connection, she might have had a different approach to magic. Maybe she would be more confident in her natural abilities rather than relying so much on study. In the fight against Voldemort, she could have used her family's resources and connections. For example, she might have known about secret Black family spells or artifacts that could have been useful. Her relationship with Snape would also be very different. Since Snape had a history with the Black family, he might have treated her with more respect or more animosity, depending on how the story was written.
Hermione could become more attuned to the darker aspects of magic. With Remus being a werewolf and Sirius having his own dark family history, she might explore the gray areas of magic more. For example, she could study more about the dark arts not to practice them, but to understand how to better defend against them. This would be a significant shift from her canon character who mostly stuck to the 'light' side of magic study.
Maybe they'd have to save their family from a common enemy. Since they are siblings in this fanfiction, their family could be in danger from a being that wants to use their combined powers. This would lead them on an adventure through both the wizarding world and the world of Greek gods, having to use Hermione's knowledge of spells and Percy's ability to navigate the world of the gods to keep their family safe.
They'd likely have a complex relationship. At first, they might be at odds because of their different initial beliefs. Draco's brought up in a family with pure - blood - centric views, while Hermione is a Muggle - born who believes in equality. But as they grow, they could start to understand each other more. There could be a lot of sibling banter, with Draco teasing Hermione about her Gryffindor friends, and Hermione pushing Draco to be a better person.
Perhaps they embark on a journey to find a lost magical creature. Hermione would be excited to study the creature, and Sirius would be there to protect them during the search. Along the way, they might encounter other interesting characters or face challenges that test their friendship and abilities.
One great Hermione's twin sister fanfiction is 'The Lost Twin'. It explores how the wizarding world reacts to Hermione having a secret twin. The story is full of mystery and adventure as they both navigate Hogwarts together.
One common theme is identity. Since she's Hermione's twin, the sister often struggles to define herself apart from Hermione. Another theme is friendship. Just like Hermione, her sister forms bonds with characters like Harry and Ron, but in unique ways.