Anna is the protagonist of Hazel’s favorite book An Imperial Affliction, and she serves as a tool to help the reader understand and interpret both Hazel and the book’s author, Peter Van Houten. Throughout The Fault in our Stars, Hazel sees herself reflected in Anna. She notes that although An Imperial Affliction is about a girl with terminal cancer, “it's not a cancer book.” After receiving her diagnosis, Anna defies stereotypes, and instead of raising money for cancer research, she starts “The Anna Foundation for People with Cancer Who Want to Cure Cholera.” Anna's characterization and Hazel’s response to it suggests that, like Anna, Hazel does not want her life and identity to revolve around her disease.
Hazel suspects the book ends mid-sentence because Anna either dies or becomes too sick to continue, paralleling the reality of Hazel’s own life as a terminal cancer patient. For Hazel as well as Augustus, death can strike at any time, and they must carry that burden with them every day. Hazel fixates on the book’s abrupt ending because she wants to know what happens to the other characters in the story after Anna's death. This obsession reflects Hazel's fear that her loved ones—her parents, for instance—will not be able to move on after Hazel inevitably dies.
Anna also symbolizes loss and the overwhelming power of grief. Her character is based on Van Houten's daughter, who died from leukemia when she was eight years old. He creates Anna to help him cope with his grief, enabling him to give his daughter a “second life where she got to be a teenager,” as Hazel puts it. The fact that Anna is based on Van Houten’s daughter, and that Van Houten is overcome with grief and turns to alcoholism and cruelty, would appear to answer Hazel’s question. However, in seeking this answer, Hazel comes to realize the pain her death will cause her loved ones is outweighed by the joy of knowing and loving her.