Eleven-year-old Yuki Sakane is the protagonist of Journey to Topaz. She is a Nisei (second-generation Japanese immigrant) living in Berkeley, California with her mother, father, and brother at the beginning of the story. Before the attack on Pearl Harbor, Yuki gets along well with her schoolmates and the members of her community; she is an ordinary American child. Yuki has a close relationship with Mimi Nelson and Mrs. Jamieson, the Sakane family’s white neighbors, and with Mr. Toda, an elderly Issei (first-generation Japanese immigrant) and member of their church congregation. Yuki has a special fondness for animals, including the carp in her family's pond and her beloved dog, Pepper, who she is forced to give up when the family is forcibly relocated to Tanforan. Yuki also looks up to her brother, Ken. As Ken becomes embittered by the family’s worsening circumstances, Yuki worries that she will lose him forever.

The attack on Pearl Harbor exposes Yuki to prejudice and injustice for the first time in her life. Throughout the novel, she is forced to reckon with the loss of her beloved childhood home and the unjust, uncomfortable, and dangerous conditions forced upon her in the concentration camps in Tanforan and Topaz.