A character like Severus Snape could be an interesting choice. He already has that mysterious and somewhat dark aura about him. Transforming him into a demon butler would add an extra layer of complexity to his character, and his relationship with Harry could be re - imagined in a whole new way.
One implication could be the confusion of the two fan bases. Fans of Harry Potter might be put off by seeing their beloved characters in a context that doesn't align with the original series. Similarly, Black Butler fans may not appreciate the distortion of their favorite story.
In the world of fanfiction, there are often very creative and out - of - the - box ideas. However, 'harry potter is a demon black butler fanfiction' seems more like a misappropriation. Harry Potter is about a boy wizard's journey through a magical school and his fight against the dark lord. Black Butler is about a young noble and his demon butler. Mixing them in this way just doesn't fit well.
One idea could be that the demon butler is secretly protecting Harry from a new, unknown dark force in Hogwarts. He uses his demonic powers to sense danger before it arrives.
Yes, there might be some fanfiction that has such an interesting and rather unique concept. Some fanfic writers like to create crossovers and put unexpected twists in them. They might imagine Harry Potter as a cat within the world of Black Butler for various reasons, like exploring different character dynamics or just for the fun of it.
In Harry Potter fanfiction, a cat could be a magical familiar. For example, it might be a cat that can transform into a wizard's assistant when needed. In Black Butler fanfiction, a cat could be part of the Victorian - era setting, perhaps a stray that Ciel and Sebastian encounter on the streets of London.
Dobby could be a great butler. He was always eager to serve Harry and was very loyal. His knowledge of the Malfoy manor and other wizarding households could be useful. And his unique brand of magic, like his ability to apparate in and out of places where other wizards couldn't, would add an interesting dynamic to the story.
One idea could be a crossover where the characters from Harry Potter end up in the world of Black Butler. For example, Harry, Hermione and Ron could be mistaken for some kind of strange magical beings in the Victorian era of Black Butler. They might be brought to the Phantomhive manor and Sebastian has to figure out what to do with them. Maybe they are there to solve a mystery that involves both the magic of the Harry Potter world and the dark secrets in the Black Butler universe.
Dobby could be a great character as a butler in fanfiction. He already has a strong loyalty to Harry and his self - sacrificing nature would make him an excellent butler. He could use his house - elf magic to keep Harry's living quarters clean and protected.
Another theme is the moral grayness. Both universes have characters that exist in that morally ambiguous area. Fanfictions tend to play with this, like when characters from Harry Potter are faced with the more cut - throat and often morally complex situations in the Black Butler world. For example, how would Harry react to some of the deals and sacrifices that are common in the Black Butler world? It makes for some really thought - provoking reading.