Harumi Kuromura, approximately six years old during these events, is the daughter of widowed Keiko Kuromura and niece of Suzu Urano. Residing with her mother in Kure at the Hojo family home after their bereavement, Harumi possesses brown hair styled in an ear-length hime cut, black eyes, and distinctive freckles. Her brother Hisao lives in Shimonoseki with their paternal grandparents; before their separation, he taught her about warships, igniting a fascination with identifying naval vessels in Kure's waters. This interest reveals a tomboyish streak beneath her girlish demeanor, fueling her own dream of becoming a sailor.

Despite Keiko's initial coldness toward Suzu, Harumi forms a close bond with her aunt. Her presence brings moments of lightness to the household amidst wartime hardships. Tragically, during an air raid, Harumi is killed instantly by a time-delayed American bomb detonating near the Hiro Naval Arsenal while walking with Suzu – the same explosion that severs Suzu's right hand. Harumi's death devastates Keiko, who initially blames Suzu for the accident. This loss compounds Keiko's earlier separation from her son, marking another irreversible personal cost of the war on the family.