From the information provided, there were many contradictions and oppositions between Sirius and Snape. Sirius, who had been accused of betraying Harry's parents and killing Pettigrew, had become a major threat to Harry in his third year. Snape had always held a grudge against Harry's father, James Potter, and Harry's resemblance to James made Snape loathe Harry as well. Sirius was Harry's godfather and cared about Harry, but Snape saw more in Harry's eyes than in James's. This contradiction was more apparent in the incident in the Shrieking Shack at the end of Harry's third year. Snape was worried that Sirius would hurt Harry, and although Sirius was innocent, he and Snape were at odds under the circumstances. Their relationship was complicated and full of hostility, which stemmed from past grudges, different attitudes towards Harry, and personal loathing. Harry Potter and the Goblet of Fire was not enough. Everyone, please click to read the novel!
I haven't come across a 'snape is sirius slave' fanfiction myself. Fanfiction themes can be very diverse, but this one seems rather unorthodox and might not be as common. However, the world of fanfiction is vast, and new works are being created all the time, so it's possible that someone has written it, but it may be difficult to find.
In some fanfictions, Sirius might be portrayed as delusional about Snape due to their long - standing enmity in the original story. Sirius has always suspected Snape of being a Death Eater, and this suspicion could be exaggerated in fanfiction, making him seem delusional.
One common theme is redemption. Many fanfics explore the idea of Snape or Sirius finding a way to redeem themselves in the eyes of the other. For example, Snape might do something heroic to earn Sirius' respect.
Yes, there are some out there. You can start by looking on fanfiction websites like Archive of Our Own. Just search for the tags related to Snape being Sirius' master and you might find some interesting stories.
There are some. But when looking for them, be aware that the 'lemon' tag usually means there will be sexual or romantic situations that might not be suitable for all audiences. Some popular fanfiction websites might have a good selection, but always respect the rules and guidelines of the site.
A common theme is redemption. Both Snape and Sirius have complex pasts with many mistakes. Fanfictions often explore how they can redeem themselves in each other's eyes or in the eyes of the wizarding community.
Sirius and Harry had a kinship. He regarded Harry as his own family, and his love for Harry was based on family feelings and the deep feelings of missing Harry's parents. He longed to live with Harry and give him the warmth of a family. Snape's feelings for Harry were even more complicated. He loved Harry's mother, Lily, and his love for Lily extended to protect Harry. Although he appeared to be strict and even harsh to Harry, he had always been secretly protecting Harry. This was a responsibility and protection that stemmed from his deep affection for Lily. It was difficult to simply compare Sirius's love for Harry with Snape's. Their love for Harry had different origins and manifestations. Sirius's love was more of a direct familial concern, while Snape's love was hidden under the stern appearance, and more of a guardian derived from his persistent love for Lily. Harry Potter and the Order of the Phoenix is not enough. Please click to read the novel!
Sirius bullying Snape may have had something to do with Snape's interest in the Dark Arts. At the time, this may have been seen as an unusual behavior and was targeted by Sirius and others. Furthermore, Sirius and James Potter were a little lacking in self-control during their school days, and might have behaved in a manner similar to school bullying. Part of Snape's dislike of Harry stemmed from Harry's resemblance to James Potter, which also reflected the conflict between James Potter (Sirius's good friend) and Snape. Sirius, as a good friend of James Potter, might also bully Snape. Harry Potter and the Goblet of Fire was not enough. Everyone, please click to read the novel!
I'm not sure about specific 'Snape spanks Sirius' fanfictions. However, you can try searching on popular fanfiction websites like Archive of Our Own. They have a large collection of Harry Potter - related fanfictions, and you might be able to find something there by using those keywords in the search bar.
PotterFanatic22 is another excellent author. Their fanfics usually feature unique plotlines involving Snape and Sirius. For example, one of their works has Snape and Sirius teaming up to solve a mystery that dates back to their school days.