One common theme is time - often Hermione travels back in time to meet young Sirius. Another theme is friendship. Since they are from different generations in the wizarding world, their friendship is an interesting exploration. For example, they might share knowledge about magic that the other doesn't know.
A lot of these fanfictions explore the idea of forbidden love. Hermione and Sirius come from different generations in the original series, so when he's portrayed as dark, it adds an extra layer of taboo to their relationship. Also, mystery and adventure are common. They might be on a quest together, with Sirius' dark side influencing the journey in various ways.
One common theme could be the exploration of forbidden love. Since Sirius is much older and in a different generation than Hermione in the original series, the idea of their relationship goes against the norms. Another theme might be the struggle with one's emotions. Hermione, being a rational character, lusting for Sirius could lead to her internal conflict between her logical side and her new - found emotions.
Rebellion is a common theme. Sirius comes from a traditional pure - blood family, but he rebels against their dark and prejudiced ways. Another theme is friendship, like his strong bond with James Potter, Remus Lupin and Peter Pettigrew in the Marauders.
One common theme is time - bending. Since they are from different generations, often the stories play with time travel or alternate timelines to make their relationship possible. Another theme could be the clash and then the melding of their personalities.
The theme of mentorship is also present. Sirius, with his knowledge of the wizarding world and magic, becomes a sort of mentor to Hermione. He guides her through difficult situations and helps her grow in her magical abilities. And there's the theme of loyalty. Sirius is extremely loyal to Hermione, just as he was to his friends in the past, and this loyalty drives his actions to protect her.
One common theme is the clash of different generations. Sirius is from an older generation compared to Hermione, so there are often differences in values and beliefs that create interesting conflicts.
One common theme is redemption. Sirius has had a troubled past, and Hermione could be seen as the one to help him fully redeem himself. Another theme is the power of love across different generations. Since they are from different age groups in the original series, the fanfictions might explore how love can bridge that gap.
Another theme is the exploration of their individual strengths and how they complement each other. Hermione's intelligence and Sirius's courage combine in these stories to face challenges that neither could alone. It's about how their destinies, which seem separate at first, start to merge and create something new. For example, in many fanfictions, they might work together to solve a mystery that has roots in both the past (Sirius's time) and the present (Hermione's time).
One common theme is the theme of mentorship. Sirius often takes on a mentorship role when he catches them. He uses his knowledge of the wizarding world, especially the darker aspects, to guide Harry and Hermione. Another theme is friendship. Their friendship is tested and strengthened when Sirius catches them in some kind of 'forbidden' activity. It shows how they support each other through difficult situations.
Frequently, there's a theme of Hermione's strength in the face of abuse. Even before Sirius saves her, she might be shown as trying to resist or endure. And then after being saved, her growth and how she overcomes the trauma can be a big part of the story. The relationship between Sirius and Hermione can also explore themes of mentorship, where Sirius helps her heal and become stronger.