The mood of the novel is mournful and anxious; there are moments of comfort, beauty, and even joy, but Death is always quick to remind the reader that every character's life will end, and every relationship will be torn apart by someone's death. For example, in Part 9: Homecoming, Liesel is overjoyed that Hans comes home from the war with a broken leg. Death tells the reader exactly when the happiness will end:
At 1 a.m., Liesel went to bed and Papa came in to sit with her, like he used to. She woke up several times to check that he was there, and he did not fail her.
The night was calm.
Her bed was warm and soft with contentment.
Yes, it was a great night to be Liesel Meminger, and the calm, the warm, and the soft would remain for approximately three more months. But her story lasts for six.
This scene should be nothing but "warm and soft." Hans used to sit by Liesel's bed all night to soothe her when she had nightmares. Now, there are no more nightmares. There is only the simple comfort of her Papa's presence. In fact, it is now Liesel who periodically checks on Hans through the night to make sure he is still safe at home. She and Hans seem to have come full circle.
For Liesel, the scene may be entirely "warm and soft." This kind of security is rare for her because she lives in a war zone, where she is always waiting for the other shoe to drop. Death knows too much to bask in the happiness, even now. He refuses to let the reader bask in it either. By setting a timeline on this happiest part of Liesel's life, Death makes sure that the reader understands contentment to be a precious, scarce resource. Especially when humans wage war on each other, it never lasts as long as it should. Contentment in the novel is thus always inflected with anxiety and sadness.