Maybe it's just a fun and affectionate nickname the author came up with to make their interactions more interesting.
It could be that Sirius views Hermione as having some kitten - like qualities. For example, she could be seen as curious like a kitten, always exploring new knowledge in the wizarding world. And Sirius, being an older character, might use this term to express his fondness for her in a somewhat teasing but loving way.
In the context of the fanfiction, it might be related to a specific plot point or character arc. For instance, if the story involves Sirius taking Hermione under his wing in some way, the 'kitten' nickname could symbolize his protective role over her. He might see her as a bit naive or vulnerable in some situations, similar to how one might think of a small kitten, and this name is his way of showing his concern and care.
It could be a term of endearment in the fanfiction world. Sirius might use 'kitten' to show a special, perhaps affectionate or protective, connection to Hermione.
Often, it begins with Hermione trying to help Sirius deal with his post - Azkaban trauma. She uses her knowledge and compassion to reach out to him. As he heals, he starts to see her in a new light. Their relationship then grows as they start to understand each other better. The lemon parts usually are used to explore their more passionate and private moments, which are often written in a very tender and intense way, adding a new dimension to their relationship.
One popular story might be 'Forbidden Bonds' which explores a unique relationship between them. It delves deep into their characters and how they might interact in a different way than in the original series. The author creates a lot of tension and drama, making it an engaging read.
In a Hermione and Sirius family fanfiction, Hermione might end up marrying into the Black family. Since Sirius was an important part of the Black family before his estrangement, Hermione could find herself involved in the family's complex politics and traditions. She could use her knowledge of magic and her Muggle - born perspective to challenge some of the old - fashioned ideas within the family. Sirius, on the other hand, could be like a mentor to Hermione, teaching her about the more secretive and dangerous aspects of the wizarding world that she might not have known otherwise.
There could be a fascination with power dynamics. Sirius is an older and more experienced wizard in the Harry Potter world compared to Hermione. Fanfic writers may be drawn to the idea of how his knowledge and power could interact with Hermione's intelligence and determination, thus leading to the concept of him dominating in the fanfiction. Also, it might add an element of unexpectedness or novelty to the relationship between two such different characters.
One possibility could be that Sirius sees Hermione's intelligence and determination and decides to take her under his wing. Maybe he realizes her potential and wants to protect her from the dangers in the wizarding world that he has faced himself.
If you're looking for a fanfiction with this specific scenario, you could try using more detailed search terms. For example, include the Hogwarts house Hermione belongs to in the search, or any specific events that might be related to it. Also, look for tags on fanfiction platforms that might lead you to the story you want. There are often tags for characters, locations, and relationships which can help narrow down the search.
A father - daughter like relationship could be expected. Sirius, having lost so much in his life, might see Hermione as someone he can care for and protect, much like a daughter. He could be very protective of her and give her advice on how to navigate the complex wizarding world.
In some versions, Hermione might use her advanced magic knowledge. She could have discovered a spell that counteracts the pull of the veil. Maybe she found a way to disrupt the dark magic associated with it and was able to pull Sirius back from the brink just in time.
In the best Sirius and Hermione fanfiction, the relationship between them is well - explored. It might not always be romantic; it could be a deep platonic bond. The fanfic should also fit within the general lore of the Harry Potter universe. For instance, if it involves magic, it should be consistent with the magic system in the books. And the pacing is crucial. If it's too slow, readers might get bored, but if it's too fast, important details could be missed. All these elements combined can make a Sirius and Hermione fanfiction stand out as the best.