Pretty sure that guy isn't Sebastian's previous master. I mean for starters he seems alive, and demons consume the soul of their master when the contract has ended. The only way i think it could make sense is that he's one of those zombie dolls (forgot the term)? But I doubt it.
Honestly considering the fact that he has fangs, he's probably another demon or creature of some kind.
Please, if anyone has any more of this sort of sweet sub-dom relationship works that dont include any rape or noncon or anything like that, please give me the names. I'm so tired. I've searched this site for longer than I should've, and all I get arw terrible femdoms who are assholes. I need more of this sweet, consensual reading material. Please (y゚ロ゚)y