#i dont think this strays too far from canon/what tiny tidbits of demon lore we have

[whereismymonsterlover]

I think about that demon TOO MUCH AAAAAH too many headcanons I'm going to go INSANE I will be drawing evil fairy Sebastian god bless his feminine waist and heel boots.

My headcanon for what BB!demons are at their physical foundations is a very dense emulsion of matter which surrounds their soul. That's what the black goop and mist is - their flesh made of infinitely transformable "matter", hence why they can take so many forms and materialise things. The amount of matter could be relative to a demon's power which grows with every soul they consume? I think of it like stem cells or atoms that can transmute or build into any earthly substance.

I especially like this because, with this magic logic, that first feast Sebastian prepares for Ciel would have been Sebastian's own flesh. By temporarily expending a small amount of his demonic "matter" to materialise all the food, Sebastian was polluting Ciel with that physical sin, made into nutrients in the form of badly seasoned chicken breast. I love this idea because it's like a totally other level of demonic possession.

Another thing to note is that this matter is not lost. Sebastian would be able to repossess that lost sin once he consumed the boy's soul. A similar idea to 'energy cannot be created nor destroyed' It's a little crazy but that's the physics of my headcanon lmao. Same for the manor - Sebatian has cosumed Ciel entirely without even touching his soul, as every brick sebastian laid is his transmutated flesh which he could snatch back for himself anytime he liked. It is him much more than it is 'his'.

Sebastian aims to possess as much of his contractor's life as he can. Be that with the very roof over their head or the food he fattens his cattle with; he doesn't want to risk poisoning his contractor so why not assure the quality himself? It's that traditional idea of demons "corrupting humans with sin" in a very literal way. Of course, this is made harder to achieve when Ciel orders Seb to execute things step-by-step, essentially barring him from materialising things from himself like this.

Chapter 138 (ironically this feels like im citing a bible verse) Sebastian is drawling on about how to interrpret Ciel's wishes. His little comment on 'keeping ciel inside his body' totally plays into what I'm imagining. This could even imply with my headcanon's logic that the flesh he repaired the manor with is exactly the concept he's describing in this panel - quarantining Ciel from harm within his own body.

I don't know! I hope this was interesting even if it's just food for thought. I love thinking about magic lore, especially when it's so mysterious in black butler. I also adore Sebastian for being such a different idea of what a "demon" can be. He's not a little red imp. He's not just a plotting piper mildly inconveniencing passers-by. And he isn't just a Mephistopheles archetype, though very similar. I feel like his "aesthetics", physicality and godly power really sets him apart. Idk I love that freak I wish we could kiss.

And this doesn't even scratch my ideas of his 'true form' or physical/earthly manifestation. so thats for a different post