Responses
I agree, though the answer to that is plot. I'm sure at least one or more from that group of people will be reappearing within the near future and that couldn't happen if they were all in jail.
It could also possibly be that Jumi doesn't want her parents to know, she doesn't want to get involved with those people ever again, or that it could be really expensive to press charges and have to do a bunch of legal processes. But...most likely just easier to not write that into the story..
Why the hell isn't something like reporting that situation even in the farthest of their minds? I don't know about korea, maybe it actually is all corrupted and police is worth shit there like in some action movies. But they could ask themselves for a split second at least if pressing charges for kidnapping, sexual harassment, threatening and physical violence may or may not be worth the try!