Origami cranes have since become a symbol of peace.

Daniel, a former journalist, met Sadako's 71-year-old brother, Masahiro Sasaki, who survived the bombing, at a peace event in New York in 2010. They agreed to work together to deepen understanding between the two countries, which are still divided over the question of the legitimacy of the atomic attacks.

"There are other opinions, there are other points of view, and I don't think we ever finish talking about that," Daniel said after visiting a museum at the memorial. "The important thing is to keep talking, to talk about all of it."

Daniel said in a statement that he decided to visit Hiroshima and Nagasaki because he needed to know the consequences of his grandfather's decision as part of his own efforts to help achieve a nuclear-free world. He said he hoped to hear stories from survivors about how they overcame their adversity.

Daniel also is to meet with the mayors of Hiroshima and Nagasaki and participate in discussions with students.