Sumi Urano, younger sister to Suzu Urano, lived with her family in Hiroshima's Eba district. Pre-war, she led an ordinary life, noted for her beauty and becoming the object of affection for a handsome Japanese Army officer. Conscripted under Japan's National Mobilization Law, she labored as a factory worker for the Imperial Japanese Army, contributing to the war effort.

Her life fractured irrevocably with the atomic bombing of Hiroshima on August 6, 1945. Working in the city, she survived the initial blast. Her mother, venturing into the city for supplies, was presumed killed instantly. Her father succumbed months later to radiation poisoning after falling seriously ill. Sumi escaped the devastation, fleeing westward to her grandmother's house in the rural town of Kusatsu, outside the immediate blast and radiation zones.

In the aftermath, Sumi developed severe radiation sickness symptoms: prominent purple bruise-like marks covered her body, accompanied by progressive physical deterioration. Her condition caused profound anguish when Suzu visited her in Kusatsu, revealing the family's tragedy. During this reunion, Sumi conveyed her parents' fates and expressed quiet resignation to her own illness, symbolizing the pervasive, invisible suffering inflicted on survivors.

Sumi's earlier encouragement for Suzu to return to Hiroshima for safety—unaware of the impending atomic strike—imbues her narrative with dramatic irony, underscoring wartime unpredictability. Her journey from a youthful factory worker to a radiation-poisoned survivor exemplifies civilian resilience and unseen scars in war's aftermath, clinging to fragmented family bonds.