Obviously, Sherlock himself is a very popular character. His brilliant mind and unique personality are central to the fanfiction. The little sister, of course, is also a key figure. Depending on how she's written, she can be a strong, intelligent character in her own right.
Some fanfictions might explore the little sister's backstory. Maybe she was sent away for some reason when she was younger and now she returns, bringing with her secrets from her past. This could add an element of mystery and drama to the story, as Sherlock and Watson try to figure out what she's hiding and how it relates to their current cases.
She can be a catalyst for change in fanfiction. Her presence might disrupt Sherlock's usual way of doing things. For example, if she suddenly shows up in his life, he may have to reevaluate his solitary lifestyle. In some stories, she could be the key to solving a particularly difficult mystery that Sherlock has been struggling with, perhaps because she has access to a different social circle or has a different way of thinking.
In fanfiction, Sherlock Holmes' little sister often serves as an interesting addition to the Holmesian universe. She can be portrayed in various ways. For example, she might be highly intelligent like her brother, with a unique approach to solving mysteries. Sometimes, she's a bit of a rebel, challenging the norms of Victorian society that her brother also tends to defy in his own way. Fanfic authors use her character to explore different aspects of the Holmes family dynamic and to create new and exciting storylines.
A common theme is family relationships. It often shows how the sister's relationship with Sherlock is complex, with elements of rivalry and deep affection. Another theme is her own detective skills, highlighting how she can be as sharp as Sherlock.
A common theme is the little sister being a hidden genius like her brothers. She might be involved in solving mysteries that Sherlock and Mycroft can't handle alone. Another theme is family dynamics. It explores how she fits into the already complex relationship between Sherlock and Mycroft. Also, there could be themes of protection, with her brothers being overly protective of her.
One great Sherlock little sister fanfiction is 'The Adventures of Sherlock's Little Sister'. It shows her using her own unique detective skills. Another one could be 'Sherlock's Sister: Hidden Talents', which delves into how she has been secretly helping Sherlock all along.
Well, for Sherlock and Mycroft's little sister fanfiction, I'd start by looking at specific Sherlock Holmes fan communities. Some Reddit groups dedicated to Sherlock Holmes might have threads about it. They often discuss and share fanfiction they like. Also, if you follow some Sherlock fan accounts on Twitter, they might retweet or recommend good fanfics involving this interesting concept of the little sister.
Well, they could have a protective relationship. Draco might be very protective of his little sister, shielding her from the darker aspects of the wizarding world he's involved in. For example, if there are threats from other wizarding families or the general chaos in the world, he'd stand up for her.
The Weasley family would probably play a role too. Ginny could be a role model for the little sister, especially in terms of being a strong female witch. Fred and George might teach her some of their pranks or tricks. And Mrs. Weasley could be like a second mother to her, showing her the warmth of a family. The Malfoys could also be in the story, perhaps as antagonists, creating conflict for the little sister and Harry.