Who are governed ultimately by the Prime Minister. So they do what she tells them to, ultimately making her the most important person.
https://en.wikipedia.org/wiki/Oath_of_Allegiance_(United_Kin...
Dan Carlin has a series on his podcast discussing the background of the war in Asia in 1937-1945 (https://www.dancarlin.com/product/hardcore-history-62-supern...). One of his major points about the Japanese government at the time was that the military held allegiance to the emperor, who couldn't or didn't actually do anything, rather than the civilian government. As a result, the military could do essentially anything it wanted.
That didn't end well.