The longer I think about it the more strongly I feel about aroace Sebastian
He certainly has a strong aesthetic attraction to Ciel and goes out of his way to make his appearance beautiful, but I gotta be so honest with you. I dont think Sebastian even has a libido. Intent is just on and off like a faucet and he form fits to what the other person wants, if he has motive to (as we've seen a couple times, such as with Beast)
He desires Ciel but it's Ciel's soul he craves and so Sebastian is clearly sex positive/views it as a sort of game with people when needed. It never starts with him thinking anyone is attractive
But with Ciel I'm like this is just...
An interface of sorts.
This isn't even Sebastian's true form. He's emulating. This is a compatible shell.
Physical touch/sex is way for Ciel to experience being close to him and for their physical forms to mimic what Sebastian wants without it actually being so. It's a substitute/placeholder. It's like eating when you aren't hungry but something happens to taste good so why not indulge in that chocolate bar
Ciel's body is a vessel and this is the only form he knows so Sebastian adjusts accordingly and is possibly even enthusiastic about affection and sex (people can enjoy the act without personal attraction, particular shoutout to kinky ace people), but I don't get the vibe that any craving or purely sexual attraction comes from Sebastian himself
Same goes for romantic intent. Sebastian form fits to the closest, most intimate roles he needs to fill for Ciel (which in canon I'd put it down as a really charged secret third thing) but again, I think explicitly romantic intent would have to start with Ciel and get reflected across into Sebastian who would then lean into it and let it be another way they're bound together
They belong to each other in such a striking and intimate way already that the details are sort of up to Ciel and Sebastian just mirrors him/manifests what he needs, and all human bonds just pale in comparison to how Ciel is already promised to him and how Sebastian is compelled to Ciel until the contract is up so the nature of said bonds just doesn't Matter to him as much
This is all to say aroace but sex and to a much more particular extent romance positive Sebastian ftw to me
