Supposedly, thrillers involving airplanes are not shown as in-flight movies, so as to avoid causing anxiety. There should be a similar rule that movies like Hachi: A Dog's Tale are not to be shown on airplanes, so as to avoid causing embarrassment. I'm not sure that my bawling my eyes out in the middle of a trans-Pacific flight really helped anyone. If you choked up at Marley & Me last year, you may want to keep an ambulance on stand-by for Hachi, which was unceremoniously dumped onto DVD a couple of weeks ago.
Which is not to say that the movie is cruel in any way, or harsh. It is emphatically G-rated, and contains not a single instance of violence, against human or dog. Rather, the reason for the tears is simply that, even with that awkward title, Hachi: A Dog's Tale is one of the most shamelessly effective movies I've ever seen about the bond between man and canine.