Their relationship could be one of mutual curiosity. The Muggle sister might be curious about Hermione's magical life, and Hermione might be curious about her sister's normal Muggle existence. This could lead to some really interesting exchanges between them, with the sister asking about magic and Hermione asking about Muggle things like technology or modern Muggle culture.
They could have a very protective relationship. Hermione, being a witch, would likely feel responsible for her sister. She might be over - protective, always making sure her sister is safe from any harm that could come from the wizarding world.
They might have a relationship full of secrecy. Since Hermione is part of the wizarding world and her sister is a Muggle, Hermione would have to keep a lot of things from her sister. But at the same time, they could still have a deep sisterly bond based on love and trust in other aspects of their lives.
Well, it could add a whole new layer of complexity. For example, Hermione might have to constantly protect her sister from the wizarding world's dangers while also trying to keep her Muggle life normal. This could lead to some really interesting scenarios where she has to juggle between her Hogwarts duties and her sister's well - being.
It could be a relationship full of secrecy. Since Hermione is a Muggle - born in the eyes of most of the wizarding world and Narcissa is from a pure - blood family. They might have to keep their sisterhood a secret to avoid scandal. They could communicate in hushed tones and have secret meetings, slowly building a bond based on mutual understanding and the fact that they are family despite all the differences.
They could have adventures related to magical creatures. Since Cedric is a Hufflepuff, he has an affinity for them, and Hermione's thirst for knowledge would make them a great team. Maybe they go on a quest to find a rare and endangered magical creature and try to protect it from poachers. They would use their combined skills, Cedric's charm and physical abilities and Hermione's magic and intelligence.
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.
Maybe the child has the power of mind control. Hermione is known for her strong mind and intelligence. Her child could inherit a more extreme version of this, being able to control the minds of others. This could be a very dangerous or useful power depending on how the child is raised and what their intentions are.
Well, a family secret might be that there was a love affair in the past between a Granger and a Malfoy which led to Hermione's existence in this fanfiction. Or maybe there are secrets about certain magical artifacts that the Malfoy family has been hoarding and Hermione, with her inquisitive nature, uncovers them. This could lead to a whole new plotline within the fanfiction.
In the fanfiction, Hermione and her older sister could have a complex relationship. Maybe the sister is overprotective, constantly looking out for Hermione at Hogwarts, especially with all the dangerous situations she gets into. The sister could also be a bit jealous of Hermione's academic success and magical abilities, which could lead to some sibling rivalry.
Well, they could have adventures that are more centered around protecting each other as family. In the original story, they were friends looking out for one another, but as siblings, it would be more of a family obligation. Maybe they would team up against threats specifically targeting their family line, and they would be more united in the face of danger compared to just being friends. Also, their adventures could involve helping each other with personal growth in a more family - oriented way, like Hermione helping Harry with his magic skills in a sisterly, nurturing way that might be different from how she did as a friend in the original story.
Well, the relationship might be complex. Narcissa could see Hermione as a unique asset, like an intelligent pet that she can show off or use to her advantage in some way. And Hermione might be in a position where she has to play along to survive or gain something. For example, Narcissa could be using Hermione's knowledge to further the interests of the pure - blood families, while Hermione is trying to figure out how to turn the situation to her own benefit.
She might meet her old teachers. They would be surprised to see how much she's grown and changed. And of course, her former classmates. There could be the popular girl from school who is now a bit jealous of Hermione's confidence. Or the nerdy boy who has now become a successful scientist and they can have an interesting exchange about different kinds of knowledge, magical and Muggle.