Koshika Kasū was born in Honjō Village (which merged into Oku Town in 1952, and eventually became Setouchi), Okayama Prefecture, Japan, on 16 March 1908. She got married at some point, and due to her husband’s job at the Forestry Bureau, the couple were often transferred to places such as Yamaguchi and Osaka. While living in Osaka, she worked as a seamstress in a tailor’s shop. After the Osaka air raids in 1945, the family returned to Okayama. Afterwards, while helping farmers, she contributed to the community for many years as a nutrition committee member, an educational committee member, and a welfare committee member.
Her hobby was sewing. With the help of her friends, she made an apron theater (apron used for puppet shows) that was donated to her community center library.
At the age of 99, she broke her leg, but was able to walk again after surgery.
Koshika Kasū passed away in Setouchi, Okayama Prefecture, Japan, on 2 October 2019, at the age of 111 years, 200 days.
On 18 March 2008, two days after her 100th birthday, she was presented with a letter of congratulations and a commemorative gift from the Prefecture and Setouchi City.
At the time of her death, she was the second-oldest living person in Okayama Prefecture, behind Kano Ebara.