On 6 August 1945, Hiroshima suffered the first atomic bombing in history. Records show that the bomb had killed more than 140,000 people by the end of the year. But no footage exists to show how people exposed to the heat, blast, and radiation tried to escape, met their ends, or survived. Only two surviving photos show the catastrophic scene beneath the mushroom cloud. They were taken on Miyuki Bridge three hours after the bomb was dropped. In 2015, NHK used advanced video technologies, the latest scientific expertise, and the testimonies of living survivors of the bombing to perform the first detailed analysis of the photos and turn the images into realistic video with sound and motion. Our goals were to learn what happened beneath the mushroom cloud and create a lasting visual record. We learned that two survivors of the bombing had been among more than 50 who are visible in the photos. They helped us find more than 30 others. The testimonies of the survivors guided our animation of the photos and helped bring many facts to light. More than 70 years after the atomic bombing, this documentary paints a vivid, comprehensive picture of what happened beneath the mushroom cloud.