Grave of the Fireflies (1988)

Fleeing the American fire bombing of Japan in 1945, a young boy and his even younger sister lose their immediate family, home, and belongings. They travel to a distant town to live with extended family, an aunt who neither wants them nor knows anything whatsoever about children nor basic human compassion.

Human compassion has been mostly sucked out of the whole population as a result of the war. The aunt is still exceptionally awful, but it's very much a part of the story that the community has mostly stopped helping each other because they have nothing left to give. Everybody clings to what little they still have in hope of survival. How much are you willing to offer to a neighbor, or a nephew, when you aren't even sure if you'll be able to feed your own children next week?

When tensions with the aunt grow, the boy decides the kids can run away and live on their own. The move into an abandoned shelter in a hill on the outskirts of town, and fend for themselves fine until their stockpile of rice runs out.

The boy tries in vain to get help from any adults; nobody will give him a job, money, or food. He turns to crop theft to survive. His sister falls ill, diagnosed with malnutrition by a town doctor. Nothing turns out well, everybody dies, and fireflies twinkle in the night sky.