He had a son, Hideaki Kase (1936–2022), who became a diplomatic critic in promoting Japanese WWII historical revisionism books and films.

[3] Acting as secretary to Foreign Minister Shigenori Togo, Kase had assisted in the preparation of the document formally terminating negotiations with the United States.

[1] On September 2, 1945, Kase was present as part of the Japanese delegation on board USS Missouri for the signing of the treaty of surrender in 1945.

[4] At his suggestion Foreign Minister Mamoru Shigemitsu and other civilian members of the party wore formal diplomatic attire of morning dress and top hats "because we were representing our sovereign" (an exception to this was Saburo Ota, who wore no hat and whose white suit contrasted with other civilian members' mostly black morning dress).

[4] Resuming his diplomatic career in 1954, Kase took up an appointment as chief advisor to the same foreign minister whom he had assisted at the surrender ceremony on board the USS Missouri.