Power dynamics could be a major theme. Given the idea of one being a'slave' to the other, there would likely be a lot of exploration of who has power and how it's used or abused. For example, Snape might have power over Sirius Black in this scenario, and how Sirius copes with that power imbalance.
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.
Finding such specific fanfiction can be a bit tricky. However, some fanfiction communities or forums dedicated to Harry Potter might be able to point you in the right direction. You can ask around in those places, sharing your interest in 'sirius black slave to snape fanfiction' and see if anyone has any good recommendations.
One common theme could be the struggle for freedom. Sirius, being in a'slave' situation in these fanfictions, would likely fight against the constraints placed on him. Another theme might be loyalty. Despite his difficult situation, he may still show loyalty to his friends or certain causes. And there could also be a theme of redemption, where he tries to atone for any past wrongs while in this difficult position.
The concept of 'snape is sirius slave' seems rather strange and a bit out of place. In the original Harry Potter series, Snape and Sirius are complex characters with their own storylines and relationships. This concept seems to distort their characters in a rather extreme way that doesn't really fit with the essence of the original story.
In fanfiction, Sirius Black and Severus Snape often have complex relationships. Sometimes they are portrayed as rivals, with their past grudges from Hogwarts days still lingering. Their different loyalties, Sirius to James and the Order, and Snape to Dumbledore (while being a former Death Eater), add layers of tension.
I really like 'A Different Perspective'. In this fanfic, it's set post - war. Sirius, who survived the Battle of Hogwarts, and Severus, who has been pardoned, find themselves living in the same wizarding community. The story focuses on how they both have to deal with their past traumas and how they start to interact with each other. They start off avoiding each other but are gradually drawn together by their shared experiences and the realization that they are not so different after all.
I really like 'A Different Kind of Rivalry'. It shows a unique take on the relationship between Snape and Sirius. Instead of just focusing on their enmity from the original series, it creates a scenario where they have to work together and gradually start to understand and care for each other. It's a refreshing read.
They are an interesting pairing because they are such opposites. Snape is brooding and often seen as the outcast, while Sirius is more bold and carefree. In fanfiction, it's fascinating to see how these two very different personalities could come together.
I'm not sure which specific 'Sirius Black slave fanfiction' is good. However, you can try looking on some popular fanfiction websites like Archive of Our Own. There, you can search for Sirius Black - related fanfics and then browse through the results to find ones that might interest you. Just make sure to follow the website's rules and guidelines.