In 1944, he was drafted as a crypto specialist for the Imperial Japanese Navy and stationed in Kagoshima Prefecture, Kyushu, an experience which he later dramatised in his famous novella Sakurajima, published in 1946.

[2] He came back on this experience in his latest book, Genka (Illusions) published in 1965, the year of his death.

After the war, he worked for the Sunao (素直) magazine, led by poet and social activist Shin'ichi Eguchi (1914–1979),[3] in which Sakurajima and some of his short stories were published.

Sakurajima established Umezaki as a representative of Japanese postwar literature along writers like Hiroshi Noma and Rinzō Shiina.

[1][4] The war theme later gave way to satirical stories like Boroya no shunjū,[5][6] and still later to the examination of human anxiety in modern society.