A key theme in Black Rain is the unknowable suffering endured by the people of Hiroshima. Not only are they victims of the world's first atomic bomb, but they also have no way to comprehend what has happened to them. The terrifying new technology is so little understood by the characters that they cannot understand why they are becoming sick. To them, the reality of radiation poisoning is a complete mystery. They remain on the bomb site and wander through the ruins of the city. They eat food contaminated by the radiation and wash themselves in water that has been directly affected by the bomb. To a modern audience with a better understanding of the effects of radiation, and to Shigematsu reflecting on the events in his diary, there is a sense of dramatic irony. The audience and the diary transcriber understand events and phenomena the characters in the story do not. The days immediately after the bombing are made even worse by the victims not knowing how or why they are suffering. The vacuum of information causes more suffering as people sort through the ruins of the burning city, desperate to understand what is happening to them but unable to do so.