Gen, his mother and his little sister Tomoko are the only ones of their family Nakaoka who survived the dropping of the nuclear bomb on Hiroshima. They struggle to make ends meet and are being evicted by the mother-in-law of their guest family. Gen and his adopted brother Ryuta try to earn money for the family but get in trouble with the Yakuza. When Ryuta shoots one of them he has to flee; Gen soon after realizes his little newborn sister has been kidnapped. Though he manages to find her, she dies of illness soon after. One year later, Gen meets Ryuta again who now works for the Yakuza and also the girl Katsuko, a Hibakusha, whom he teaches with his books.