I understand Miraiko is not a slave by choice. That said, if she happens to be submissive, and she honestly likes having Julia as her mistress, it's not creepy at all. If she happens to be a spy and enjoys playing the role of Julia's willing slave, it's not very creepy. Having only read prior archive entries, I suspect one of those to be true, if not both.
I'm dead certain there are worse "masters" to have in Nova Roma than Julia, but taking hold of that collar wouldn't sit well with most people... Unless it's a sexual thing, but then ick! There are children in the room!