Masako Soga was born in Kannabe (now part of the city of Fukuyama), Hiroshima Prefecture, Japan, on 23 February 1913, as the seventh of eight children. She was born small and was raised by her older brother and oldest sister, who fed her with amazake instead of breast milk. After getting married, she moved to Ibara City, Okayama Prefecture. Her husband, a film engineer, passed away in the early 1980s.

Soga was able to sew until she was 95. At the age of 110, she still had 20 of her own teeth, and still enjoyed eating her candy rice crackers. Among her favorite foods are fruits, fried chicken and pork cutlets. In April 2023, she was still able to walk, although she broke her femur at the age of 102. When asked about the secret of her longevity, she replied: “Chew food well.”