It's good to know that in a Musketeers!AU, Sebastian would be Milady. So pretty.
I don't know, would "she realises he's a vampire and wants to get him alone so she can kill him" count? They can both be completely convinced they're the one ~seducing~ the other. Or she realises he just wants information but goes along with it anyway, sure guy, you're irresistible /brings out stake