HIROSHIMA, Japan — The crowd sat entranced as 78-year-old Emiko Okada recalled the horrifying events of Aug. 6, 1945, a day that started hot and cloudless. There was the buzz of the plane, the huge flash, the cries for water, the kids like ghosts with skin dangling off them, the people with their guts hanging out. “We don’t want you young generations to go through what I did. You can help by spreading what you just heard from me to other people,” Okada – a hibakusha, or “atomic bombed person” – said this week in Hiroshima not far from the spot where American forces dropped Little Boy, the first atomic bomb to be used in warfare, 70 years ago Thursday. Not only is Okada telling her own story, but she has also begun to train an apprentice to continue disseminating her tale after she’s gone: a memory keeper, one of a growing number here being designated as an “A-bomb legacy successor” as the number of survivors dwindle. While there are still more than 183,000 survivors of Hiroshima or Nagasaki alive in Japan today, their average age is 80, according to official statistics. Okada’s designated storyteller is a 39-year-old man who works in a Tokyo department store and has no direct ties to Hiroshima.