There might be such a fanfic out there, but it's not a common or mainstream type of fanfic. Some niche or more experimental fanfic writers may have explored this idea, but it could also be that it doesn't exist at all. You could try searching with specific keywords related to 'ciel' and 'diapers' in the fanfic search engines of different websites.
Obviously, Ciel is the main character. He's the one usually in the diapers, and the story often revolves around his experiences, his emotions, and how others in the Black Butler world react to his situation.
One popular 'ciel in diapers fanfic' might be 'Ciel's Little Secret'. It explores a rather unique take on the character in a more innocent, child - like state with the diaper aspect adding an interesting twist to the story.
One possible plot could be in an alternate universe where Ciel has some sort of illness or curse that causes him to regress to a younger state where he needs to wear diapers. The story could then focus on his struggle to maintain his dignity while dealing with this new situation, and how his friends or servants help him through it.
One popular 'ciel loves ciel fanfic' could be 'Ciel's Self - Discovery'. It delves deep into Ciel's internal thoughts and feelings towards himself in a very unique way. Another might be 'The Unseen Bond between Ciels' which focuses on the unspoken connection between different versions of Ciel. There's also 'Ciel's Self - Love Journey' that shows his growth in self - acceptance and love.
Well, in non - lemon fanfic, Sebastian is often depicted as a sophisticated, powerful demon who is bound by contract to serve Ciel. Ciel is a young, determined noble with a dark past. But in lemon fanfic which is inappropriate, it may distort their characters in improper ways for the sake of adult - themed content. So it's better to focus on their proper character traits from the original source like Sebastian's loyalty (in a non - inappropriate sense) to the contract and Ciel's intelligence and drive to seek revenge.
In this fanfic, Ciel's fear of the dark might be a manifestation of his past traumas. He has endured so much at a young age, and the dark could symbolize the unknown and the things he fears from his past, like the abuse and the loss he has faced.
I'm not sure specifically about a 'ciel pregnant fanfic'. There are many fanfic platforms out there, like Archive of Our Own (AO3), but you'd need to search through their databases using relevant tags to find out if such a fanfic exists.
The 'ciel neglected fanfic' could be a work that focuses on the theme of neglect regarding a character named Ciel. It might start by introducing Ciel's situation where they are not getting the love, support or attention they deserve. This could be in a family - like setting, or within a community in the fictional world of the fanfic. As the story progresses, we might see Ciel's struggle to find their place, their feelings of loneliness and how they try to overcome this state of neglect. It could also explore how other characters around Ciel either contribute to or are oblivious to this neglect.
I'm not entirely sure specifically as it could vary greatly. 'Ciel' might refer to a character from a particular series, and a 'breakdown fanfic' could be about that character experiencing some sort of emotional or mental breakdown. It might explore the character's inner turmoil, what led to the breakdown, and how they deal with it in the context of the fan - created story.