I assumed that Ling'er's frailty was in part because of her youth. And there's nothing wrong with characters who are always on the run. For some reason I like Mason from the little I read about him and while he seems to have a bad guy vibe to him, there's also something endearing to him, mostly that he cares for Ling'er.

Chan-wook seems a little weird to me but all characters that would benefit from counseling usually win me over at some point.