i know what you mean, the first time i saw it i rented it and i swear i must have cried for at least an hour after the movie was over. it was so sad. i own it now, but i've still only watched it twice.
i remember the beginning w/ Seita in the train station, the time w/ their aunt, and in the shelter, but i can't think of anything after Setsuko dies, probably b/c i'm not even thinking about the movie anymore, just going over the "why?" of it in my head...
Grave of the Fireflies is one of the most incredible movies i have ever had the privilege of viewing.