A Japanese woman and an American man whose grandfathers experienced the U.S. atomic bombings of Hiroshima and Nagasaki from opposite sides have forged an unlikely collaboration to publish a book calling for a world free of nuclear weapons.

One co-author is Kosuzu Harada, 50, a Nagasaki resident and the granddaughter of a double hibakusha, a survivor of both the Hiroshima and Nagasaki atomic bombings. Her collaborator is Ari Beser, 37, the grandson of a radar operator who flew aboard the U.S. B-29 bombers — Enola Gay, which dropped an atomic bomb on Hiroshima on Aug. 6, 1945, and Bockscar, which released one on Nagasaki three days later.

Published in July, their book is titled "Kinokogumo no Ue to Shita no Monogatari" (Stories from Above and Below the Mushroom Clouds). It carries the English subtitle "From above and below both mushroom clouds, we became friends."