Little is known about Sumako's life before she meets Masao. Her marriage to Masao is arranged, a matter of convenience for their families. During Sumako and Masao’s first attempts to have children, she suffers two miscarriages. Both babies are boys.
In July 2002, she and Masao try for a child a third time. She carries the baby to full term and on April 23, 2003, she finally gives birth to a girl they name Mako. Throughout Mako's childhood, Sumako doted on her daughter. One of Mako's fondest memories is of her mother brushing her hair.
On the day Onibaba made landfall in Tokyo, Sumako takes Masao to the city to receive treatment for his cancer. After his appointment, Masao and Sumako take their daughter shopping and buy her a pair of red shoes. Their visit to the park coincided with Onibaba's attack. Masao and Sumako lose their daughter in the crowd during the rush to escape the Kaiju. Sumako and Masao are killed by the Kaiju, leaving Mako on her own.