Greetings! This is definitely an interesting question, and one which deals with a fairly wide scope of time in the past 50 years or so. For the sake of brevity (or at least, some brevity), this response shall deal mainly with the US Occupation of Japan and a minor aside here and there about its foreign policies and geopolitical role during the Cold War which followed. Note that this is by no means a completely comprehensive or exhaustive look at the transformation of post-war Japan and its role in the Cold War, but it should serve as a general overview of what transpired after the surrender onboard the USS Missouri on September 2nd, 1945. Let's begin.

Notes: part of this response, mainly the ones which deal with the immediate post-war settlement and Occupation of Japan, have been adapted from previous comments of mine on AH. All of these are linked, for further reading, in the "Sources" section.

A Nation in Turmoil

“Despite the best that has been done by everyone--the gallant fighting of our military and naval forces, the diligence and assiduity of out servants of the State and the devoted service of our 100,000,000 people--the war situation has developed not necessarily to Japan's advantage, while the general trends of the world have all turned against her interest.”

- Emperor Hirohito in the "Jewel Voice Broadcast" on August 15th, 1945.

When the Emperor took to the airwaves to announce the Japanese surrender to the Allies, it came like a "bolt from the blue", as many had been kept in the dark about the course of the war, and news of the atomic bombings of Hiroshima and Nagasaki had not yet become nation-wide knowledge. The decision to surrender (according to the Emperor's speech) included the atomic bombings, and the general turning of the war's course against Japan's favour. When the news broke to the public, many were uncertain as to what would happen to Japan in the coming years, and what this surrender meant for the future of them and the country. Others however, claimed that the time had come for Japan's "rebirth", when it could shake off the authoritarian and militaristic "corruption" that had started the war and chart a bold new course in the postwar order. Historian Andrew Gordon on this mix of individual moods:

"Some of his stunned listeners would later recall that August noon as an instant of 'rebirth'. For these people, the surrender was a moment when past experience and values were rendered illegitimate. They decided to chart a totally new course, whether personal, on behalf of a national community, or both. Other listeners, already struggling to find food and shelter in bombed-out cities, fell into a condition of despair and passivity. Still others—especially those in positions of power—resolved to defend the world they knew. Despite the shared national experience of defeat, individual experience varied greatly."

For the military who had kept Japan's war machine turning throughout the long years of war and prior to it, the news of surrender was quite literally fatal. An estimated 350 officers committed suicide in the hours after the Jewel Voice broadcast, although they remained a very minor group in a sea of passive acceptors. The dark legacies of the war's impact played out in the days before the official Japanese surrender onboard the USS Missouri on September 2nd.

Bonfires around Tokyo destroyed any evidence of wartime activities which might be used against the government and military. The planning of official "comfort stations" began on August 18th, and by year's end thousands of women were serving Allied soldiers in "Recreation and Amusement Centers", in an effort to protect the "purity" of the Japanese race from foreign blood (the Occupation authorities outlawed these stations in January 1946, but permitted privately-licensed brothels to continue operations). The government feared that the imperial institutions which had shaped Japan into a modern state would be swept away by the occupying powers, replaced by "state socialism" akin to that which they believed was applied in the USSR (though in this instance, it was the US which they feared would be the revolutionary vanguard).

The late Japanese historian Mikiso Hane, in summarising the impact of the end of the Second World War on Japan, writes:

"[in 1945] all the beliefs and values [the Japanese] had been taught since childhood were shattered...The Japanese people were reduced to ground zero in their moral, intellectual, and spiritual life."

By the time the American occupiers had come ashore in September 1945, they had been vested with the authority and power to impose sweeping reforms on the Japanese nation, akin to those that had marked the Meiji Restoration of the 1860s. When the head of the American occupation forces, General Douglas MacArthur, came to Japan, he would assume a new role which arguably commanded even more authority than the Japanese government itself: SCAP, or Supreme Commander of the Allied Powers. With a Japanese government in turmoil, a people whose national identity had been thrown into chaos, and an economy in shambles, MacArthur and his men had a fair bit of work ahead of them.

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