Masao Tomonaga is the honorary director of the Japanese Red Cross Nagasaki Atomic Bomb Hospital and a hibakusha, an atomic bomb survivor. He studied internal medicine and hematology at the Nagasaki University Medical School. Currently, he runs a retirement home for older hibakusha. In this interview, Dr. Tomonaga discusses his experience surviving the bombing of Nagasaki. He outlines the immediate physical impacts the bomb had on people’s bodies, the long-term physical impacts, such as cancer, and the psychological harm. He also discusses the simulation Japan’s Ministry of Foreign Affairs conducted to see what a one-megaton nuclear detonation would look like in a modern city today.