SanCom has been getting a lot of token audio webm lately, but they are just that. Audio for the sake of it. It doesn't match with the animation besides in setting.
Looks like some type of seal or magic circle. I don't know, haven't seen this anime series/game series/whatever before.
In the series, the main character (her) is supposed to act undercover inside a underground city brothel. But they didn't know that all the girls in the brothel were to be given magical seals on the mouth, which forced them to obey every command otherwise the seal will kill them.