Yes, it's certainly commendable to base a story on such complex themes and at least, the mangaka managed to get it right when dealing with the relations between Jin and Lee-Ren.
However, the reasons why a victim of sex abuse and child rape(what else could it be when a man purchases a child slave?) would choose to bind himself to his abuser(s) are never fully explored nor explained clearly. Was there a reason for Lee-Ren's loyalty(supposed fear that the father would try to harm his family or Jin) or did the years of abuse give birth to a craving for pain and unhealthy desires? Or did he simply try to tell himself that he deserved it or even try to explain away the abuse?
And in a long-term relationship of abuse, the victim often becomes the abuser and there's usually a power play between the victim and the aggressor or a third or fourth party. Did Lee-Ren pave this road or did he simply remain the victim, choosing never to heap abuse on others?
CJ Michalski at least gets this right in Kowarekake no Omocha but in this story, everything is a bit too one-sided and though the plot was good, there're too many assumptions made. The mangaka almost hits the spot in defining how abuse could shape one's relations with others(like how some tend to misinterpret that the victim wants to be saved, without any proper discussion) but there're a few misses.
Update To Yeunchi: You might be right but the thing is: did the mangaka at any time point that out? Well, much of it is left to the reader to assume and to supposedly draw his/her observations from various historical accounts.
To me, if one aims to tackle such topics, you need to tightly restrict your storytelling devices to steer people to the exact topic. Otherwise, the writer risks having more than 20 versions inferred from the story, with many missing the point while some get it. You see, you get all of it while all of my friends didn’t. And we’re supposed to study tons of history just to see from the author’s viewpoints? You’ve got to be kidding, right? 😛