One main theme could be innocence. The kitten represents pure and untainted innocence in contrast to the often dark and morally complex world of 'Black Butler'.
One interesting 'Black Butler Kitten Stories' could be about a kitten that somehow gets involved in the affairs of the Phantomhive household. Maybe it wanders into the mansion and starts causing little mischiefs that Sebastien has to deal with while still attending to Ciel's needs.
One tickle story could be when Sebastian might playfully tickle Ciel as a way to amuse him during a less tense moment. Maybe when Ciel is feeling a bit down and Sebastian uses tickling to cheer him up, making Ciel giggle despite his usually serious demeanor.
As far as I know, there are no official tickle - related events in a very direct sense. However, the characters do have moments of light - heartedness and playfulness that could potentially involve tickling in fan interpretations.
One interesting story is about how Sebastian, the demon butler, always manages to fulfill Ciel's requests in the most extraordinary ways. For example, when Ciel has to attend a dangerous social event, Sebastian uses his demonic powers subtly to protect Ciel while still maintaining the appearance of normalcy.
The story of how Ciel made a contract with Sebastian is quite memorable. Ciel, in his quest for revenge after the death of his parents, sold his soul to Sebastian in exchange for help in achieving his vengeance. It's a dark and compelling start to the series.
Another important character is Grell Sutcliff. He's a reaper. Grell has a flamboyant personality and his own goals and desires which often intersect with the affairs of Ciel and Sebastian. His presence adds a lot of chaos and mystery to the 'Black Butler stories'.
If the story is about kindness towards animals, the moral could be that we should be kind and take care of all living beings, like how the characters in the story took care of the black kitten.
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.