Here is everything you ever wanted to know about the Japanese emperor, daimyo, shogun and samurai. It is a long book, but tells the lore of the legendary rulers from about 500 B.C., as well as the recorded historical information up to the Showa period.
The institution of the Japanes emperor is an ancient one and central to understanding Japan. This general readership book outlines the history of the Japanese emperor through its history and eclipse by the Shoguns and later restoration in modern times.
Originally published in the 80s, this is obviously out of date in the later chapters.
That out of the way, Packard has laid out the history of Japan's monarchy from the very beginning, through to his modern day. The focus remains tight on emperor and court, so thise looking for a wider history of Japan's government's actions are in the wrong book.
Packard examines the place Japan has given its emperors - as religious leaders - and how that has and hasn't shaped the rest of the country. It is a really interesting read of such a different kind of power.