Another theme is the power of love and brotherhood. The fanfictions often show how Sirius' love and care for Regulus can overcome the barriers of the Black family's dark heritage and the dangerous magical world they live in. It's about how that connection between the two brothers can be a source of strength in difficult times.
There's also a fanfic titled 'A Brother's Love'. In this, Sirius' care for Regulus is shown through various heart - warming and tense situations. It shows how Sirius tries to protect Regulus from the dark path the family wants him to take.
One great fanfiction where Sirius Black takes care of Hermione could be 'The Guardian'. In this story, Sirius steps in when Hermione is in a difficult situation at Hogwarts. He becomes like a mentor to her, protecting her from the threats of the dark forces that are starting to lurk around the school. He teaches her some advanced magic that she wouldn't have learned otherwise.
Protection is also a big theme. Given Sirius' nature, he feels a sense of responsibility to keep Hermione safe. This could be from dark wizards or from the general dangers that lurk in the wizarding world. Sometimes, it's about protecting her reputation or her place at Hogwarts too.
Fanfiction about these three can take many forms. For example, there could be time - travel fics where Harry goes back in time and meets Regulus and Sirius when they were younger. This could lead to all sorts of interesting plot twists, like Harry trying to prevent Regulus from joining the Death Eaters in the first place. Or it could be a fic where Sirius survives and he and Harry explore the secrets of the Black family together, including things that Regulus left behind. There are also fics that focus on the emotional bonds between the characters, showing how the different personalities of Regulus, Sirius, and Harry interact and influence each other.
One common theme is family loyalty and betrayal. Since they come from the Black family, their actions towards each other and the family are often explored. For example, Sirius leaving the family while Regulus had a different path within it.
The themes often revolve around the idea of secrets. Regulus may be hiding secrets from Sirius, which ultimately lead to his departure. This can create a sense of mystery and suspense in the fanfiction. Another theme is the power of choice. Regulus makes a choice to leave, and this choice has far - reaching consequences for both him and Sirius. It can also explore the theme of redemption. If Regulus has made some wrong choices, his leaving could be a step towards redeeming himself, either in his own eyes or in Sirius's eyes. Additionally, the theme of the impact of the wizarding war on personal relationships is quite common, as their situation may be a microcosm of the larger conflicts and divisions in the wizarding world.
Well, it's popular mainly due to the characters involved. Sirius and Regulus are both interesting characters from the Harry Potter universe. The concept of Sirius adopting Regulus creates a lot of drama and emotion. It's a chance to explore what could have been if things were different in their family. There are so many possibilities for plot twists and character interactions in this scenario, which draws in a lot of readers.
One common theme is family loyalty. Sirius is driven by his love for his brother and his sense of family duty to save Regulus. It shows that no matter how estranged they may seem, family bonds are strong.
Another element is the mentorship. Sirius imparts his knowledge of magic, especially the less - taught or more dangerous aspects like dark magic counter - spells. He also gives her advice on how to navigate the complex wizarding society. In some stories, he helps Hermione understand the history of pure - blood mania and how to combat it. This mentorship helps Hermione grow not only as a witch but also as a person in the wizarding world.