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.
Eric x Alan fanfics in the Kuroshitsuji fandom can be really interesting. They often explore the relationship between these two characters in unique ways. Some fanfics might focus on their backstories, like how they came to be in the world of Kuroshitsuji. Others could delve into their emotional connection, perhaps a deep friendship or something more. It really depends on the writer's interpretation of the characters and the world they've created within the fanfic.
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 of the best places to find Eric x Alan Kuroshitsuji fanfic is Archive of Our Own (AO3). It has a large collection of fanfics from various fandoms, including Kuroshitsuji. You can simply search for 'Eric x Alan' in the search bar and filter the results for Kuroshitsuji. Another option is Fanfiction.net, although the interface and tagging system might be a bit different. There are also some Tumblr blogs dedicated to Kuroshitsuji fanfic that might have Eric x Alan stories.
One interesting Naruto x Kuroshitsuji fanfiction could be 'The Crossover Chronicles'. It combines the unique ninja world of Naruto with the dark and mysterious setting of Kuroshitsuji. In this fic, Naruto somehow ends up in the world of Kuroshitsuji and has to navigate the complex social and supernatural hierarchies there. Another great one is 'Naruto in the Black Butler's World' which focuses on how Naruto's skills and values clash and blend with the characters in Kuroshitsuji.