Sadako is an energetic, 11-year-old girl living in Hiroshima, Japan, nine years after the atomic bomb was dropped on her city. Known for her speed and athleticism, she spends her time training with the goal of joining the junior high school track team. After experiencing unexpected dizzy spells following a school relay race, she is diagnosed with leukemia, which forces her into a lengthy hospital stay. Relying on her natural optimism, she adopts a traditional legend and begins folding 1,000 origami cranes to earn a wish for a miraculous recovery.

Chizuko is Sadako's best friend, a bond they have shared since kindergarten. In contrast to Sadako's fast-paced energy, Chizuko maintains a slow, steady, and thoughtful demeanor. Although she does not personally believe in legends or good luck charms, she introduces Sadako to the story of the paper cranes and folds the first golden crane for her.

Mr. Sasaki is Sadako's father, who works diligently as a barber to support his wife and four children. He is a proud and devout man who instills strong values and a sense of duty in his family, regularly honoring their ancestors. He takes particular pride in Sadako's athletic abilities while trying to maintain a brave, reassuring front regarding her health condition.

Mrs. Sasaki is Sadako's caring and self-sacrificing mother. She manages the busy household and worries over her daughter's boundless energy, later spending extensive time visiting Sadako at the hospital. Despite the family's financial limitations, she prioritizes her daughter's comfort by purchasing special foods and sewing traditional garments.

Kenji is a quiet, nine-year-old boy also receiving treatment for leukemia at the Hiroshima Red Cross Hospital. Orphaned and primarily cared for by an elderly aunt, he spends much of his time in solitary reflection. Unlike Sadako, he views his medical condition with quiet resignation and relies on his chart readings rather than legends or miracles.

Masahiro is Sadako's 14-year-old older brother. He occasionally teases her about her superstitions, such as her belief that spiders bring good luck. Despite his teasing, he actively supports her during her hospitalization by bringing her homework and hanging her origami cranes from the ceiling.

Mitsue is Sadako's nine-year-old younger sister. She shares in the household chores and looks up to her older siblings, joining the family in their daily routines and hospital visits.

Eiji is the youngest child in the Sasaki family at six years old. He provides small moments of levity for the family and contributes to Sadako's crane-folding efforts by sending her a silver candy wrapper to fold.

Nurse Yasunaga is a caregiver at the hospital where Sadako is treated for leukemia. She encourages her young patients to hold onto hope, actively utilizing the paper cranes as a tool to comfort Sadako during difficult moments on the ward.

Oba Chan is Sadako's late grandmother, who was killed by the atomic bomb. Though deceased before the novel begins, she remains an active presence in the family's life through daily prayers and holidays like O Bon, representing the enduring nature of familial memory.