Power dynamics is another frequent theme. Given Sebastian's demonic nature and Ciel's position as his master, many fanfictions play around with how power is balanced, negotiated, and sometimes subverted between them.
The dark and gothic atmosphere of the 'Black Butler' world is also a prevalent theme. Writers love to recreate and expand on the spooky and mysterious elements, like the supernatural occurrences and the Victorian - era setting.
One common theme is the exploration of gender roles. Since Sebastian is male in the original, making her female flips the traditional power dynamics. Another theme is often romance. A female Sebastian might have different romantic interactions compared to the male version. Also, there's the theme of identity as she tries to fit into the world while being a different gender.
One common theme is loyalty. Even when being tortured, Sebastian's loyalty to Ciel often comes into play, either as a driving force to endure the torture or as something that is questioned by the torturer.
A prevalent theme is the exploration of innocence. The child character's innocence is contrasted with the dark and often morally ambiguous world of Black Butler, with Sebastian playing a role in either maintaining or corrupting that innocence. For example, some fanfictions might show Sebastian trying to shield the child from the harsher realities of the underworld, while others might show him using the child's naivete for his own ends. Also, the theme of family or surrogate family can be found. The relationship between Sebastian and the child can be developed in a way that mimics a father - son or older brother - younger sibling dynamic, adding an interesting layer to the story.
Love and loyalty are common themes. Since Sebastian is a demon, his relationship with his mate often involves a complex exploration of these emotions. The mate has to deal with his demonic nature while still maintaining love and loyalty.
In 'Black Butler Sebastian x Claude fanfic', one of the main themes is the exploration of their complex personalities. They are both mysterious and have their own motives. This is often explored in detail. Another theme is the idea of loyalty. Their loyalty to their masters can create interesting conflicts and situations. And a third common theme is the concept of the supernatural world they inhabit. The rules and hierarchies of the demon world are often part of the stories.
One common theme is family loyalty. Since it's about Sebastian's sister, her loyalty to Sebastian or vice versa is often explored. For example, in many fanfics, she will go to great lengths to protect him or keep his secrets.
One common theme is the power imbalance. Sebastian is a powerful demon, and Ciel is a young, mortal master. This creates a lot of tension and interesting situations where Ciel is constantly trying to hold his own against Sebastian. Another theme is loyalty and its limits. Sebastian is bound by a contract, but his true motives are often questioned.
The theme of sacrifice also shows up a lot. Ciel may sacrifice his own humanity in order to achieve his goals, and Sebastian may sacrifice his own freedom in a way by being bound to Ciel. And there's always the theme of the supernatural, with Sebastian being a demon and all the dark magic and otherworldly elements that come with that in the fanfics.
A common theme is their rivalry. In the original Black Butler series, Sebastian and Claude are butlers with different motives, and this often translates into intense competition in fanfictions. They might compete for their masters' attention or for some powerful object.
In Black Butler Claude x Sebastian fanfiction, a common theme is the exploration of their demonic natures. Writers often delve into how their demon instincts interact with their relationships. Also, themes of loyalty and betrayal are popular. For instance, what would make one of them betray their master for the other? It's all about the complex web of relationships and power dynamics that make these characters so interesting in fanfiction.