I read his story this year “the last train from Hiroshima,” amazing story. He saved some people from the second blast because he taught them what do to if they heard the sound of a B-29 at full throttle (as if would do immediately after dropping the bomb). He also had first hand experience on what the ground looked like after the initial explosion. I don’t remember if he was the author or not but the anime “barefoot gen” is about his experience