During the Shogunate, the government in Edo pursued a policy of curbing the powerful feudal lords. One technique was to require them to maintain a home in Edo and house their wives and children there. This kept them in the capital much of the time, and left hostages when they were absent. Denjirô Ôkôchi is one such lord; while he is gone, local power is wielded by..... call him a majordomo.
Another technique was to limit the size of the warships the domains could build. Ôkôchi's majordomo has ordered the building of a warship above the limit. Another feudal lord has already built such a warship ad seen himself and his clan broken.
It's a tale of competing tyrannies, the ability of the majordomo to order things that will get everyone killed, and the efforts of his wiser advisors to forestall him.... when he can order them to kill themselves whenever he chooses. The artistic impulse of this movie are obscure to me. The shogunate's rules are there to maintain its unchallenged authority, but is that tyranny of which the audience should disapprove? Certainly, the shogun's handling seems arbitrary and thoughtless, that of a man drunk on his power to command. Alas, this seems to me a story about the Japanese being very Japanese, and little more, even as I am convinced that it is indeed a lot more than that.
