The understanding of the movie *SPOILERS*
The movie can be understood in a lot of ways I believe. But is there any right way to understand it? I'll show you my interpretation:
The whole movie didn't have any deep meaning until the very end. The subtitles in the end really show you what the whole moral of the story is. The sentence that explains what morage (i think) is - the time when you stop mourning - puts the whole concept into the movie.
It really shows you... how you actually never stop mourning. The ones you love never really die in heart. There was no escape for the main characters in the end. Shigeki saw his end... and when he dug into the place where it is supposed to be Maki's spirit, he knew that he is going to die there. He was happy that he'll finally reunite with his love. Machiko somehow cried and was sad at first... but then she started to laugh.. so this could mean that she found her peace, she found her mo-rage. It was in the same spot as Shigeki's. In death.
That is only my interpretation.. But i'd be delighted if you put your own down here..
Extraordinary expectations made me humble.