And many require opinions as answers.
I’ll give you my own quick take. The big cultural change for Japan came when Admiral Perry of the USA arrived in the 1850s. He pretty much opened the country to outside influence by force. This shock was the main cause for the civil war that happened in Japan thereafter, in which the supporters of feudalism lost. Japan wanted to become more European and more powerful–it turned more to England and Germany than to the US for advice and influence.
Japan successfully militarized and built up its economy and industry–one of the great success stories in human history.
Then Japan won the Russo-Japanese war in 1904 or so (the peace was brokered by Teddy Roosevelt, who won the Nobel Peace Prize for doing so). It had defeated a major European power; it had arrived. The military and protofascist philosophy of the government had been validated. Japan went on to fight on the side of the Allies in WWI, battling its future parter in crime Germany in the Pacific.
Around this time, Japan started becoming not such a nice country. It took over Korea in 1910 and Taiwan around that time. By the 1930s, Japan was building an empire in Asia. It took over huge chunks of China (the Nanking Rape occurred in 1937). Despite the absolute horror of Nanking, things settled down in China rather quickly, and there was an uneasy but reasonable status quo in place. (At this time there were coups and little chunks of chaos in Japan itself. There was a fairly strong Communist contingent.)
Then WWII. But things could have turned out otherwise. The 1940 Olympics were scheduled to be played in Tokyo but were cancelled because of WWII. The relationship between Japan and the US was chilly, but the point of no return had not been reached. If you look at Japanese movies from the 1930s, you see the same Art Deco Euro aethetic that you do in US films. You have nice music, books critical of the war in China (Ikite iru Heitai by Tatsuzo Ishikawa, which was eventually banned), etc. Sure, you had fascism and all the emperor sh*t, but my impression of Japan at the time (including Japanese culture) is not one of absolute madness. It was nothing like Nazi Germany.
So, Japan lost the war, and the culture that appeared directly after it is not so radically different than what you see today, and my guess is that it’s not so different than what was before it. Our grandma here talks about life in Tokyo before the war. It was not so wild or weird.
Personally, I view the whole fascism/militarism thing as being a failed experiment that really didn’t reflect the base culture. Japan had never been expansionist before the 20th century, and there had been relative political stability under the shogunate for hundreds of years. Sure, it was a narrow-minded, insular, xenophobic country with some weird military traditions (samurai and whatnot).
I don’t know–that’s my spin. Like anything else, it’s an egregious oversimplification.