Well, a Kuroshitsuji Sebastian x Reader fanfic often explores the relationship between the reader and Sebastian. It can range from romantic encounters to adventures they might have together. The allure of Sebastian's character, with his dark charm and loyalty to Ciel, makes for an interesting dynamic when paired with an original reader - inserted character.
One common theme is the power dynamic. Sebastian is a powerful demon and the reader is often in a more vulnerable position, so exploring how that power is balanced or shifted is frequent. For example, in many fics, the reader might initially be at Sebastian's mercy but gradually gain some form of influence over him.
One common theme is the forbidden love. Since Sebastian is a demon, a relationship with a human (the reader) is against the natural order. Another theme could be the power dynamic, as Sebastian has a lot of power and the reader may be in a more vulnerable position. And of course, there's the theme of mystery, as Sebastian's true motives and the nature of his relationship with the reader are often explored.
There's also 'In the Demon's Embrace'. This fanfic is known for its vivid descriptions. It shows how the reader character interacts with Sebastian in the dark and mysterious world of 'Kuroshitsuji'. It plays on the allure of Sebastian while also exploring the reader's own journey within this fictional realm.
There's a fanfic called 'The Meeting of Shadows' which is quite interesting. In this story, Sebastian and Claude are forced to work together on a task by some mysterious force. It shows how they interact when they have a common goal, while still maintaining their enmity. It's a great read if you like exploring their dynamic.
The relationship in 'kuroshitsuji ciel x sebastian fanfic' can be seen as a twisted form of symbiosis. Ciel, having lost so much, uses Sebastian's demonic powers to achieve his goals. Sebastian, on the other hand, patiently waits for Ciel's soul. There are moments of tension and trust between them. For example, in various situations, Ciel has to trust Sebastian to get him out of danger, and Sebastian has to follow Ciel's orders, which sometimes put his own 'demonic code' to the test.
One popular trope is the 'Forbidden Love' aspect. Since Sebastian is a demon and Ciel is a human, their relationship can be seen as something that goes against the natural order. Another is the 'Power Struggle' trope. Ciel may try to assert his authority over Sebastian, but Sebastian's demonic nature gives him an edge in certain situations. 'Soul Bond' is also common. Given their contract and the connection it implies, fanfictions often explore the deeper spiritual and emotional bond that might develop between them.
One common theme is the power dynamic. Ciel, as a human, has power over Sebastian in the sense of their contract, but Sebastian's demonic powers far exceed Ciel's. Another theme is loyalty and betrayal. There's always the underlying question of whether Sebastian will truly fulfill the contract or if he might find a way to betray Ciel. Also, the theme of revenge is prominent as Ciel is seeking revenge for his family's death and Sebastian is a key part of that journey.
In the Kuroshitsuji world, there is a lot of mystery surrounding these two characters. Fanfiction allows readers and writers to dig deeper into their backstories and what might be going on in their minds. The idea of Sebastian and Claude together in a fanfic can also create some really unique and engaging plot twists, as they are not characters who would typically be on the same side in the original series. This makes for a very exciting exploration of their relationship in fan - created stories.
Some fanfictions explore the concept of Sebastian's true nature as a demon and how it affects Ciel. For example, his demonic abilities might both protect and endanger Ciel at the same time. The theme of revenge also comes up a lot. Ciel's quest for revenge and how Sebastian aids him in it can be a central plot. There's also the theme of sacrifice. Whether it's Ciel sacrificing something to keep Sebastian by his side or vice versa, it adds an interesting layer to the stories.