Ciel is a complex character in these fanfictions. He is often depicted as cunning and calculating, using his wits to navigate the dangerous world of the Black Butler. Doll, on the other hand, is more of a free - spirited character, at least initially. She was part of the circus which was a world away from Ciel's aristocratic life. Their interactions are what drive the fanfictions forward.
In some fanfictions, Doll might have a change of heart about Ciel after seeing his vulnerability. For example, she could find out about his past traumas and decide to protect him instead of being on the opposite side as her circus troupe was initially. This could lead to a complex relationship development between them.
Definitely not. The Black Butler series has a set of established themes such as the supernatural elements, the Victorian - era setting, and the complex character relationships. The idea of a 'leashed slave story' is completely foreign to the official canon and is likely a disturbing creation outside of the proper series. It would go against the overall tone and moral framework of the official work.
There is indeed a 'Black Butler' visual novel. It features the same dark and alluring art style as the anime and manga. The visual novel might include different storylines, some of which could be exclusive to this format, providing a new perspective on the 'Black Butler' world. It often has a strong focus on character development and the complex relationships within the story, which is great for fans who want to explore more about the characters.