Matsutani was born in Tokyo, Japan on February 14, 1926. She was the youngest child of , a lawyer and politician. She was an avid reader. She graduated from high school in 1943. However, because her father died when she was 11 years old, her family could not afford to send her to college. Instead, she worked at a bank called Nihon Kangyō Ginkō and the Japan Travel Bureau. In 1945, during the Bombing of Tokyo that occurred during World War II, her family evacuated to the city of Nakano in Nagano prefecture. While there she met , who mentored her as a writer.
