Grave of the Fireflies is probably the saddest anime I've seen.  It starts with a dying boy in a train station in Kobe.  A small candy container lies next to him, and the janitor who finds him tosses out into the nearby field.  Fireflies fly around it and ghostly images of the boy and a little girl appear and flashes back to a short time eariler.  The 14-year-old Seita and his 4-year-old sister, Setsuko, lost their mother during a fire-bomb attack on their city, and their father is out in the battle field.  They had an aunt who took care of them, but even the kids became a nuisance her family and soon Seita and Setsuko leave the family to survive on their own.  They settled in an abandoned bomb shelter.  At first, they had some money in the bank, but soon they found themselves out of food.  Being malnutritioned, Setsuko became really weak and Seita had to risk his life and steal during air raids in order to feed themselves.  Seita found out that the war was over yet there was no sign of their father's return.  Realizing that they were truly orphans now, they were really on their own to survive.  Despite the effort, Setsuko died, and Seita had to take care of her funeral arrangement and try to keep himself alive...

The anime is very quiet and the conversation is not deep.   The focus is the interaction between the sibling and how they faced their situation.  The bond between the siblings were strong and Seita tried his best to take care of his little sister, but his abilities were limited.  This is a depressing anime that shows the helplessness of a teenager who tries to keep his little sister and himself alive during the war and after the war.