I know a lot of people don’t like to admit that season 2 exists, but you have to admit that it allows for some interesting scenarios that modern AUs do not allow. That being said, I would like you to consider a couple post-season 2 scenarios:
Scenario A: Ciel and Sebastian get along eventually and they decide to form a band; more specifically, one that has a sound something along the lines of symphonic metal.
Sebastian is the singer/lead guitarist and Ciel plays violin; they recruit a couple humans to play bass and drums and maybe another instrument or two. With Ciel’s newly acquired grace and skill, violin playing becomes so much easier and actually quite enjoyable and so many of the instrumental portions of their songs consist of wickedly difficult and impressive violin and guitar duets. Sebastian’s vocals are equally impressive: he can go from a low bass to soaring falsettos in the blink of an eye, not to mention particularly demonic-sounding growls and shrieks.
On stage, Sebastian will wear his signature heels, leather pants, the occasional leather vest, and nothing else. Ciel will wear an elaborate Victorian or steampunk style outfit onstage. The rest of the band wears whatever they like, whether it be simple or something that fits in with what the two demons wear, although it’s usually the latter. There are inevitably endless hell and devil puns and the rest of the band get sick of it real quick.
Scenario B: Ciel and Sebastian get along eventually and live in an apartment together and make youtube videos.
Sebastian makes haul videos, as well as various fashion and style videos, including makeup videos. He will also occasionally make videos about fashions from various time periods in history and show them off, both men and women’s fashion. His subscribers think he’s very dedicated to educating people about fashion, but for Sebastian procuring an outfit is as easy as breathing.
Ciel is an avid gamer in the modern world so he makes let’s play videos with a focus on horror games. (It’s mostly so he can laugh at them because what’s a horror game to a demon?) What makes him popular are the rants he goes on when he’s irritated. When he gets /really/ pissed at the game he’s playing, Victorian era slang will get peppered in and his fans think it’s incredibly adorable and that it’s part of his shtick. Also, Ciel frequently has to buy new keyboards and mice because he’ll mash the buttons too hard and break them.
Sometimes Ciel and Sebastian will record videos at the same time and Sebastian will hear Ciel yelling from the other room and yell back, “Kid, I’m trying to make a video here” and Ciel yells, “you can fuck right off m8″. Sebastian will edit these instances out of his videos, but Ciel won’t and this makes for some interesting rumors once people figure out they live together. Once all the rumors get sorted out, Sebastian will occasionally join Ciel when he does livestreams and the ensuing conversations are hysterical, such as the following:
“You’re not doing very well on this level.”
“Do you think you can do any better, Sebastian?"
"Do you want to try?"
"Would you like me to?"
"Fuck no, this is my livestream."
"Watch your language, Ciel."
"You’re not my mum, Sebastian. My mum is dead."
"See what I deal with every day? Such an insolent child."
"Shut up Sebastian, you’re distract- GOD DAMN IT SEBASTIAN YOU MADE ME DIE AGAIN!” And then you can hear Sebastian laughing as Ciel curses at him.