One common theme is the exploration of Ciel's relationship with Sebastian as a demon. How their contract changes and how Ciel adapts to his new demonic nature. Another theme is Ciel's struggle for power in the underworld, as he is now a demon. It often involves him facing other powerful demons.
Another theme is the struggle between Ciel's human side and his demonic nature. Fanfics may show him grappling with his emotions, memories, and moral compass in the face of his transformation. For example, he might question his past actions and how they fit into his new identity. It makes for a very interesting character study.
One common theme is Ciel's revenge. Since his backstory in the original series is about seeking revenge, many fanfictions explore this further. Another is his relationship with Sebastian, so there are a lot of fanfictions that focus on their master - servant dynamic in different situations.
One popular theme is the complex relationship between Ciel and Sebastian. It often explores the power dynamics, with Sebastian being a demon bound to serve Ciel. Another theme is the dark and mysterious world they inhabit. Many fanfictions delve into the supernatural elements of the Black Butler universe, like the existence of other demons and their motives. Also, the idea of Ciel's revenge and how Sebastian aids him in that quest is a common theme. It shows how their goals are intertwined despite their very different natures.
One common theme is identity. Since Ciel already has a complex identity, adding a twin doubles that complexity. Another theme is family, exploring the relationship between the twins and how it affects their actions.
One common theme is the exploration of gender roles. Since Ciel is female in these fanfictions, it often shows how she defies or conforms to the Victorian era's expectations of women while dealing with the underworld and supernatural elements. For example, she might have to balance her ladylike image with the need to be a strong and decisive leader like the male Ciel was.
Family or surrogate family is also a theme. Given Ciel's tragic family situation in the original, fanfictions may introduce new characters or develop existing relationships in a way that gives baby Ciel a sense of family. For instance, some stories might have the servants of the manor taking on more parental roles towards the baby Ciel, creating a warm and loving environment for him to grow in.
One common theme is mystery. Ciel's eye is already quite mysterious in the original work, and fanfictions often delve deeper into it. For example, they might explore the origin of its power in more detail.
In Black Butler Alois x Ciel fanfiction, a frequent theme is the idea of redemption. Despite their often cruel actions, some fanfictions try to show a path of redemption for either or both of them. Also, the theme of rivalry is common. They compete for various things, like influence in the underworld or the loyalty of certain characters. And there's the theme of emotional turmoil, as both Alois and Ciel have deep - seated emotions that are often in conflict with each other.
One common theme is loyalty. Finny's unwavering loyalty to Ciel is often a central aspect. Another theme could be protection. Finny protecting Ciel from various threats, be it other supernatural beings or human enemies. Also, growth is a theme. Ciel might grow as a person because of his interactions with Finny, learning about emotions like trust and kindness that he may not have fully understood before.
One common theme is the vulnerability of Ciel. When he's sick, his usually strong and stoic facade crumbles, and we see a more human side of him. Another theme is the loyalty of his servants. They go to great lengths to care for him, highlighting the bond they have. For example, Sebastian might use his demonic powers in a different way to heal Ciel rather than just for his usual tasks.