One challenge could be living up to their parents' expectations. If they come from a family with a long magical lineage, there might be pressure on both of them to be top students or powerful wizards. James might feel overshadowed by Hermione's academic achievements, or Hermione could feel left out when James gets more attention for his daredevil stunts.
A third plot could be centered around their different friend groups. James is likely to be friends with more mischievous types, while Hermione has her studious friends. Their sibling relationship could be tested when their friends' actions or opinions clash. But in the end, they realize that family is more important and find a way to bring their two worlds together.
In fanfiction, James is often portrayed as confident and a bit of a daredevil. He might be more open - minded towards new magical ideas. Hermione, on the other hand, is still the brilliant and studious witch. She uses her vast knowledge to solve problems. For example, in some fanfictions, James might be the one to pull Hermione out of her books and into an adventure, while she uses her logic to keep them out of too much trouble.
I really liked 'Sibling Rivalry in the Wizarding World'. In this fanfic, Hermione and Draco as siblings have some intense moments. Their different personalities lead to some great plotlines. For example, Hermione's studious nature clashes with Draco's more laid - back and sometimes snobbish attitude, but at the end of the day, they still have that sibling bond that holds them together.
Another theme is the idea of family loyalty. Despite their differences, they are siblings. So, they often have to defend each other against others at Hogwarts. In some fanfictions, they might be in a situation where Draco is being bullied by other Slytherins for having a Muggle - born sister, and he has to decide whether to side with his house or his sister. And Hermione might have to deal with her Gryffindor friends not understanding why she's related to a Malfoy.
I really like 'Darker Ties'. In this fanfiction, the idea of Harry and Hermione being siblings is explored in a very unique way. There are a lot of plot twists. For example, their family history is intertwined with some dark secrets of the wizarding world. It's a page - turner as you keep wondering how their relationship as siblings will evolve in the face of all these revelations.
Lucius has a sense of entitlement that comes from his pure - blood upbringing and family wealth. Hermione, being a Muggle - born (in the original story), has had to fight for her place in the wizarding world. So in fanfiction as siblings, Lucius might initially look down on Hermione's more inclusive views, while Hermione would be appalled by Lucius's prejudice. However, as the story progresses, they could learn from each other. Lucius could become more open - minded and Hermione could understand the pressures of a pure - blood family.
One interesting plot could be them discovering their relation later in life. For example, Hermione might be adopted without knowing her true family ties. Then, through some magical mystery, she finds out she's related to Lucius. It could lead to a lot of inner turmoil for both of them as they come from very different worlds within the wizarding community.
Often, Hermione uses her vast knowledge of magic. For example, she might use a time - turning spell, like in many fics. This allows her to go back to the time when James and Lily were in danger and interfere to save them.
One great Hermione, James Potter and Lily Potter fanfiction is 'The Unlikely Trio'. It explores a unique alternate universe where Hermione time - travels and gets involved in the lives of James and Lily. The story is full of interesting character interactions and a well - crafted plot that keeps you hooked from start to finish.