Itsuka Ōshimo was born as the only daughter of a farmer in Akitakata City, Hiroshima Prefecture on December 12, 1908. She got married around the age of 20 and she gave birth to 4 children (two sons and two daughters). Her husband was adopted into the Ōshimo family, so she never changed her maiden name. The couple lived in Osaka after their marriage, but when she was 38, they returned to Akitakata and took over her family farming business.

One of her hobbies was reading – she especially liked thick literary magazines. She had no foods she disliked and especially liked after-dinner desserts and to drink jellies and juices that were handmade by her family. She had no particular medical history other than cataract surgery when she was around 80 years old.

Ōshimo drove an electric three-wheel senior car and enjoyed playing gateball until her 90s. At the age of 105, she moved to the nursing home. Prior to that, she lived with her family at her home. Her family said that Itsuka always cared about her family and was devoted to them.

Ōshimo died in Akitakata, Hiroshima Prefecture, Japan, at 13:42 of 22 August 2021, at the age of 112 years, 253 days. As of February 2023, three of her children were still alive: the eldest son (aged 92), the eldest daughter (aged 90), and the second daughter (aged 88).