I don’t know too much about the details of Koo Gum. I haven’t seen it but the case with Japan and China is the Massacre of Nanking, China where Imperial Japan sent their troops over to Nanking and mutilated/slaughtered children, women and men off the whole city. Many Chinese have not forgiven...
I was slightly surprised with the teaser. It has so much cgi and action. I expected more romance, but it was mostly action pack filled with cgi and fantasy? Kind of not what I expected.