William T. Spears is also quite popular. His strict and no - nonsense attitude provides a great contrast to other more chaotic characters, and fanfiction often plays with his interactions with other reapers or the main Black Butler characters.
Ronald Knox is another popular reaper in fanfiction. His laid - back yet efficient nature can be used in various ways in fan - created stories, such as getting involved in unexpected adventures or having unique relationships with other characters.
Ciel is definitely one of the most popular. His complex personality and his tragic backstory make him a great focus for fanfiction. Writers can explore his inner thoughts and feelings more deeply. Sebastian is also very popular. His demonic nature and his loyalty (in a rather twisted way) to Ciel are fascinating aspects to write about. Grell is another popular character. His flamboyant and somewhat deranged personality offers a lot of room for creativity in fanfiction.
Grell is quite popular as well. His over - the - top personality and his unorthodox views make for some really entertaining reaction scenarios. He can go from being overly dramatic to having some surprisingly deep insights in fanfiction.
Ciel Phantomhive is often paired with the twins in fanfiction. Since he is a central character in the Black Butler series, writers like to explore different dynamics between him and the twins, such as a power struggle or a forced alliance.
In addition to the main characters, characters like Finny, the gardener with his superhuman strength, can be interesting to feature. Fanfiction can explore his backstory more deeply, like how he got his powers and how he copes with being different. Bardroy, the chef, is also a character that can add a lot to a story. His military past and his rather unique cooking skills (or lack thereof) can be a source of great stories in fanfiction.
Sebastian is often very popular. His demonic charm and loyalty to Ciel, despite his ulterior motives, make him a fascinating character to write about. Fanfiction writers can explore his internal struggles between his demonic nature and his growing attachment to Ciel.
Hermione Granger often appears in crossovers. Her intelligence and magical abilities from the Harry Potter series can be paired well with the more gothic and dangerous world of Black Butler. For instance, she might use her knowledge to outwit the demons or help Ciel solve a difficult case that has a magical element to it.
Ciel is also very popular. Picture a scenario where Ciel finds a cat and decides to keep it. The dynamic between him, a young noble with a dark past, and the cat can create some really heart - warming or suspenseful moments. The cat could either be a source of comfort for Ciel or bring new challenges to his already complex life.
Sebastian is always popular. In Black Butler Stainless fanfiction, he could be portrayed as having a special connection to stainless - steel objects, perhaps using them in his demonic tasks in a unique way.
I think Sebastian and Ciel are the top contenders for the most popular characters. Sebastian's allure lies in his demon - like qualities, his ability to get things done, and his loyalty (even if it's in a rather dark way). In real - life fanfics, he can be a character that people both fear and admire. Ciel, on the other hand, has that relatable aspect of someone who has been through a lot and is trying to regain control. His journey in a real - life adaptation can be very engaging, and many fanfic writers like to explore different aspects of his character.
Ciel and Sebastian are usually the most popular. Ciel with his cool and calculating demeanor, even in a high school setting, is quite appealing. And Sebastian, with his charm, loyalty to Ciel, and his many skills, always draws a lot of attention. People love to see how they interact with the high school environment and other characters.