These are indeed matters of basic Japanese history as GP claims, although I’m not too sure whether “basic Japanese history” is actually common knowledges except for Japanese history majors or someone who has gone through Japanese compulsory education.

Wikipedia article on Shogun[1] has a nice quick summary on pre-modern Shogunate system. It’s similar to British constitutional monarchy in a sense: the emperor was to delegate all power to the government and was to remain within instructions and supervisions of the government.

1: https://en.wikipedia.org/wiki/Shogun