Reddit reviews Japonius Tyrannus: The Japanese Warlord Oda Nobunaga Reconsidered (Japonica Neerlandica)

Honestly, this question is really just asking "hey, could you retell the main narrative of Japanese history for 1000 years?" It's kind of like asking "What's the relationship between the Pope and European Kings and Queens?" and it should probably be in popular questions. I mean honestly just read any textbook, since this relationship is the central political question at any point from 1200 onwards. It's not in popular questions and this would make a crappy /r/askhistorians post though, so I'll go ahead and link-filled summarize:

It depends on what time period you're talking about. Since you explicitly asked for shogun/emperor, I'll start with the first shogunate. Established in Kamakura (symbolically, far away in the traditional lands of the Minamoto clan instead of in Kyoto where the Emperor was) in 1192 as a result of the Gempei war, it stripped the emperor of most of his temporal power. Even at that point, though, the operative power was not in the Emperor himself, but rather his courtiers (see the fujiwara clan), as the Emperor himself spent most his time fulfilling the many Shinto-Daoist rituals that were cosmologically needed to keep the realm in working order (a lot of waving stuff around, purifying stuff, burning stuff, etc.) The war was really between to rival warrior families who were desperately trying to marry into the courtiers and eventually the Imperial family itself. One won, the other lost, and the winner set up an alternate power structure. From here on, power fluctuated between a few sources. At some points, Emperors would 'retire' to become monks, leave their sons to do the ritual crap, while they exercised some measure of power
from the monastery (no small irony there). In this period, around 1340, after another short war/power struggle, the Ashikaga family deposed the Kamakura shogunate and set up their own shogunate within Kyoto itself. Depending on who was shogun and who was cloistered, real power fluctuated. Sometimes even abbots of powerful temples would get in the mix. In terms of actual family ties, all 3 groups were closely linked and regularly intermarried. For a really good monograph on this interesting period, I'd see Gates of Power by Adolphson.

By the late 1400s, though, that system was breaking down altogether. Local Samurai basically acted on their own perogatives on their own land. At this point, the Sengoku Jidai (age of country at war), there are people claiming this and that in terms of rulership, and all of it is meaningless. The only thing that mattered was military strength and personal loyalty, which could be broken at the drop of a hat if the benefits were seen to outweigh the consequence. For this period, the history shelf is littered with colorful picture books about the HONORABLE SAMURAI WARRIOR and all kinds of nonsense (it is also when Shogun: Total War (and its re-make) is set). One trustworthy monograph on the ending throes, that I'd say also captures the essence of the period, would be Japonius Tyrannus by Jeroen Lamers.

The Tokugawa Shogunate, set up by the eventual victor in 1600 onwards, sought to solidify sole control. During the wars, the great temples had been almost completely obliterated, so they were out. The Shogunate removed the other threat to their power, the Imperial Court, by taking over administration and funding of the Imperial Household (and thus removing the powerful courtiers that traditionally surrounded the Emperor together). In order to leave the Emperor to his important ritual business, they very kindly removed from his household the burden of managing any land--making them completely dependent and unable to cultivate their own powerbase. While the Emperor was still seen as the ultimate source of both political and cultural legitimacy, temporal power was seen to have been devolved entirely to the Tokugawa family (who did still regularly marry daughters off to Emperors). With the Royal Baby in our thoughts, I'd say it's similar to how the UK runs now; the Emperor is around, popular, and beloved, but not even a figurehead in terms of running things. A good window into how things ran in the middle of the period would be The Dog Shogun by Beatrice Bodart-Bailey.

This is, until the "Opening of Japan" leads to everyone going nuts. For the Boshin war and what follows, I did write a post about that here just a few days ago. One thing I didn't link to in that is a book about all the neat intellectual history, which really touches on your question in terms of how intellectuals built up a sense of legitimacy for the Imperial Restoration and how that leads up to the revolution, so I'll link it here: Before the Nation by Susan Burns.

What kind of depth and detail are you looking for? A sure bet to start with is surely the Cambridge History of Japan series.

I enjoyed this book, but the price is wicked high apparently and I had the luxury of interlibrary loans. Oda Nobunaga isn't as popular in English-language literature because he's overshadowed by the Tokugawa shogunate that came after and Toyotomi Hideyoshi, unfortunately, and there's actually a great deal of Japanese and Chinese literature on the subject that never gets translated. Luckily, most works about Tokugawa Ieyasu and Toyotomi Hideyoshi will involve Oda Nobunaga, so you an always go that route.

I am assuming you can't read Japanese.

Reading Materials:

Chronicles of Oda Nobunaga. Primary source record by one of his vassals.
Description of Japan Primary source by Jesuit Luis Frois comparing Japan and Europe.

Japonius Tyrannus by Jeroen Lamers on Oda Nobunaga

Hideyoshi (Harvard East Asian Monographs) on Hideyoshi and Shogun: The Life of Tokugawa Ieyasu (Tuttle Classics) on Tokugawa Ieyasu. These are outdated but I'd recommend anyone else other than Stephen Turnbull.

Speaking of Turnbull, everyone else please look in The Samurai Sourcebook and Samurai Commanders. The only reason I'm putting Turnbull on the list is there seem to be no other English sources. Just remember Turnbull takes propaganda, fiction, and rumor at face value (interestingly he says Sadler did, but Sadler's book is oooooold) and from time to time have outright mistakes. If he talks tactics, ninjas, backroom politics, or conversations without citing a primary or Japanese secondary source, use the information with caution. Also IIRC most of his general numbers (ie numbers he produce without saying which primary source they're from) is can be traced back to Meiji Imperial Army book which is not accurate.

I might get back to you with the others if I get around to it, but as the request is large and I'm super busy lately I'll just leave you with a roundabout translation/paraphrase of Frois' description of Nobunaga:
>He is of average height, slender, little mustache, and has a high voice. He likes war and is constantly focused on training for war. He is very proud and very strict in delivering justice. If someone dishonours him he will without a doubt get revenge, but sometimes he displays a human and merciful side. He sleeps little and gets up early. He is not greedy, is decisive and very experienced at warfare. He [can be] incredibly impetuous and frantic but is not always so. He barely listens to the advice of his vassals, and all greatly respect him. He doesn't drink, eats little, is incredibly frank to others, and is arrogant about his own opinion. He looks down on all the other princes of Japan, and speaks to them as if they're subordinates. Everyone obeys him like an absolute monarch. Even when the fortunes of war are against him, he's calm and great at enduring hardship. He has great reason and judgement, and treats any kind of rites to God, the Buddha, pagan divination or superstition with disdain. In name at first he acts as if he belongs to Hokke Sect (Nichren Buddhism), but after attaining greatness he looks down on all idols. In a few points he follows Zen Buddhism and does not believe in the immortality of the soul or rewards and punishments in the afterlife. His house is incredibly clean, and he is incredibly meticulous in everything. He hates protracting in conversations and long preludes, and talks friendly even with lowly servants. He likes famous tea bowls, horses, swords, falconry, and really likes sumo wrestling. No one is allowed to wear weapons before him. He has a slight depressed look. Even when he meets difficulty he is fearless. Everyone obeys his every word.