If you want a happy ending, dont watch the last 5min. Stop, when in the bamboo forest the FL is danceing in the snowfall and the ML is watching her. Stop there, and this great story will not get ruined.
This is a beautiful story, a cute couple. A beautiful description of an emerging love, a love which for you sacrifice your life. Then the last three minutes slap the viewer with the worst possible ending. I hope there will be a special ending with a happy ending, because this is the worst ending they could have come up with.