The Book Thief
Tools of Characterization
The name Hubermann is telling. It turns into "Human" when we remove a few letters, and also sounds, as a New York Times reviewer points out, like "über-man," "über" meaning something like "best" (source). Although that Times reviewer sees Hans in particular as "implausibly saintly" and doesn't have kind words for Rosa, we think they are some pretty good humans. They provide shelter and kindness for many foster children, and risk everything to try to help Max.
Meminger, Liesel's last name, seems like a combination of "memory" and "messenger." It's easy to see Liesel as both a preserver of memory, through her writing, and a messenger of good things, including the words from books. Memory is also painful for Liesel, since so many are her memories are about people who are dead. Her name helps highlight these aspects of her character.
Thoughts and Opinions
In Nazi Germany, your thoughts and opinions define you. As we note in "Character Roles" there aren't any big antagonist among the main characters. The antagonist is Nazi ideology. The characters' refusal to subscribe to Nazi ideology, and their courage in actively resisting such ideology, makes them highly sympathetic characters. As the novel points out, Germans of this sort were rare, at least at the beginning of the war. Ninety percent of the voting public subscribed to Hitler's way of thinking. This helps us see just how strong Liesel and her friends are, so strong they will risk everything to live according to their own beliefs about right and wrong.
Almost everybody in the novel is defined, to some degree or other, by fighting. This can be literal fist fighting, in the case of Max, who dreams of boxing matches with Hitler, or fighting for survival. For Hans, Rosa, Liesel, and Rudy, it means fighting against the system in place around them in so many ways. For Death, fighting, in terms of the raging war, means more work and more mourning humans left to haunt him.