Based on the true story of Sadako Sasaki. Sadako lived in Hiroshima during World War II. On August 6, 1945, the United States dropped the atomic bomb about one mile away from her home. Sadako was only two years old.

When Sadako was 12, she became very sick. Her neck and the area behind her rears started to swell. A year later, purple spots began forming on her legs. She was eventually diagnosed with leukemia, which her mother referred to as "atom bomb disease)." In February of 1955, Sadako was hospitalized and told she had one year, at the most, to live.