John Hersey's writing style in Hiroshima is rather precise. While following a chronological narrative (meaning in order of which things happened), the text offers distinct details, vivid imagery, and true human emotion. Given that the text follows the characters for forty years, the text needs to possess both structure in time and characterization.
In the opening chapter, Hersey's narrator explicitly details the characters the text will follow. Nothing is left out. The mannerisms and physical attributes of the characters are given. Hersey's narrator (omniscient) knows everything about each of the characters the text follows.
Hersey seems to take a realistic approach, offering details on the bombing with an observational and unattached hand. This could unnerve some readers given the lack of affect the narrator seems to have. The novel's writing, blatant and clinical, should shock most readers given it mirrors the lack of compassion many have associated with the bombings.