Yeah, but the male goon slaves who attacked the priestess also had the same necklace, and as far as I'm concerned they had no powers they had to subdue with it, so it's probably just there to coerce them into submission. It is probably some mimd control aparatus that messes with the head of it's subjects to some degree, while also apparently inhibiting their powers. A side effect of that may be the fact that Ryoko keeps calling Ryo her master. My likelier theory, as a veteran who has played this game from around the first if not first version, is however that the story was originally that Ryoko was supposed to be a runaway slave (there are plenty of indicators that will likely be reworked when Ncrow gets around to do it) and she has ptsd, which has now been retconned to the story we know today. The master thing may stick around if Ncrow is into it, I suppose, personally I don't mind, but I get that some people may do.
Well it may be like that with those that attacked the priestess since the master orders them, so they had to obey the will who controls them, as with Ryoko is different case as above said, the person did nothing like that that may initiate her obey the will of the person who wears it for her, and yes i not mention what the necklace do too that is revealed ofc later by Natsuki (about her body being more mature shhh.).