After spending their childhood with the grandmother, the dog and the granddaughter were able to sleep only if the grandmother promised to meet them in the morning. The death of their grandmother made their lives unbearably sad. They continue to live with memories of her and the hope that they will see her again when they wake up.
The story is about loss and the terrible pain that comes with it. Getting used to the fact that you might never see the person ever again and, if you don't believe in afterlife, then the only thing left to comfort you are the memories of the person.