The Spring of Rage and the Tokyo Wall
The Korean War backfired horrifically on one individual who hadn't even vocally supported it, Prime Minister Hatoyama of Japan. His failure to explicitly prohibit the war outraged much of the Japanese center and left, which remained still staunchly anti-war. Even though the Communists were thoroughly chased from respectable politics having been officially banned, this simply caused many Communists members to infiltrate the still-legal Japan Socialist Party, which commanded the allegiance of most of Japan's publicly unionized workers, such as the teacher's unions. The Siege of Seoul and stories of civilian deaths sparked massive antiwar protests that overran Kyoto, Osaka, Hiroshima, Fukuoka, and Tokyo (at least the South Japanese parts). In addition, although Japan was not directly involved in the war outside of shipping assistance, it was a primary military exporter (of steel, gears, widgets, and what not) to South Korea, and industrial Japanese workers regularly engaged in the sabotage of factories perceived to be producing war material. Finally, most worryingly to the government, 4/5ths of Japan's Korean population was affiliated with the North (as opposed to the South).[1] This was interestingly not based on ideology, but rather the geographic origin of Korean-Japanese.
The protests in Tokyo were estimated to be the largest mass protest in Japanese history, with over half a million marchers, even larger than the previous Communist general strike during the US occupation. The protesters included both radical Communists and more conventional, but still radical socialists, but the pictures of hammer and sickles especially alarmed the South Japanese government, which was further put on edge by the mobilization of the Soviet Army in North Japan to the border. Some also theorized that some people just went to the protests because it coincided perfectly with cherry blossom season, causing the protest movement to largely adopt cherry blossoms as their motif. Cherry blossoms however, have been associated also with the fleeting nature of life ever since the famous invocation of cherry blossoms in the Tale of Heike, an ill omen that was to shortly come true. Acting under orders of the Kim Il-Sung government, North Korean-aligned Korean-Japanese provocateurs launched attacks on Japanese police during the Tokyo Protests. A terrified local police force acting under the orders of former National Police Force commander Takushiro Hattori, operating without Hatoyama's direct orders, immediately responded with force.
Tokyo exploded in rage, soon followed by Kyoto, the city in Japan with the most former Communists. The students immediately became the most radical, attacking police officers on sights with Molotov cocktails and other improvised weapons. Massive streetbrawls exploded, especially as construction workers on Tokyo's increasingly intricate subway system (privately unionized workers were a bastion of support for Hatoyama) went off work on their own initiative to fight both students and members of the Japan's railway unions (a well-known Communist bastion of support).[2] The construction unions generally had close relations with Tokyo's Yakuza groups, which caused many Yakuza members to join in the violence. Very quickly, Tokyo's subway system had to be shut down in order to curb the violence, but this didn't stop agitators on both sides from using the metros tunnels as ways to ambush their enemies. Corpses notably began to pile up in the Ginza and Marunouchi Lines, which would have to be eventually removed to re-open the subways. However, the anti-war protestors had their own advantages. Much to the consternation of Japanese police, protestors could sneak into the Communist sector of Tokyo (namely, Tokyo east of the Arakawa River.) In addition, most of Japan's teachers went on strike just before the start of the school year on April 1st, causing a nationwide school stoppage that further polarized the nation. The radical nature of university students caused most colleges in the country to similarly shut down.
Hatoyama was horrified by the violence, a direct challenge to his dream of a liberal, united, egalitarian society. Instead of responding nationally, Hatoyama decided to hunker down. He told worried comrades in his Social Nationalist Party (SNP) that the best way to not further divide Japanese society was to remain neutral in both the war and protests, wait for the South Koreans to triumph, and watch as the protest movement ebbed away. Hatoyama felt very confident about this approach up until the point the People's Liberation Army entered the war and destroyed almost the entire South Korean Army in roughly a month and half.
The news of the ROK Army's destruction basically doomed Hatoyama's premiership, as his allies on the political right indicated that they no longer had confidence in Hatoyama's ability to continue. The Social Democratic wing of the Social Nationalist Party under Suehiro Nishio, Jotaro Kawakami, and Tetsu Katayama supported Hatoyama, but he had lost the support of the liberals under Hitoshi Ashida and Tanzan Ishibashi, as well as the conservatives under Nobusuke Kishi and Mamoru Shigemitsu. Hatoyama immediately resigned and retired from politics, confident that he would be succeeded by either Ishibashi or Shigemitsu, both of whom promptly became too ill to run for election. In a shock to all parties involved, Nobusuke Kishi won the leadership election on a platform of clamping down on the Communist rioters with force.
Police forces were marshaled from outside of Tokyo, often staffed by far more politically conservative rural police forces who were in a mood to crack heads. Kishi genuinely considered the option of going to war, but ultimately decided against it after realizing he didn't have the support in his own party to do so. However, he was sick of Communist rioters dodging across the border to East Tokyo where South Japanese police could not pursue, and then coming back later far-better armed. Working with his allies in various Yakuza groups, Kishi came across a simple solution: building a giant wall to isolate East Tokyo. Kishi-aligned construction workers immediately began constructing what would become known as the Tokyo Wall, quickly putting an end to this trend. In addition, Kishi quickly became best friends with President Richard Russell, greatly deepening the US relationship. The two of them began hammering out a possible mutual defense treaty between the country, something only put on hold due to Russell's challenging re-election campaign.
Due to much harsher repression, the death toll rapidly climbed, destroying much of Tokyo's shopping centers due to mass brawling, looting, and gunfire. Protestors rapidly stepped up the degree of violence, often ambushing police officers and soldiers to deadly effect. However, after the declaration of a ceasefire in the Korean War, the anti-war protesters quickly began to disperse, having made their point and feeling emboldened over preventing Japanese intervention in the Korean War. Schools and subways and shops began reopening. However, images of street violence, including pictures of police officers gunning down student protesters, quickly became seared into the minds of Japanese popular culture. Kishi quickly became known as the "Showa Devil" for his harsh repression, which eroded much of his support outside of the right-wing of the Social Nationalist Party. The Spring of Rage, referred to by left-leaning Japanese as the Tokyo Massacre, is estimated by some to have claimed somewhere between 10,000-20,000 lives, including around 500 Japanese soldiers and police officers.
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[1] OTL, this was 2/3rds, but with a more southern border that puts Seoul in the North, this is 4/5ths.
[2] This is OTL - they once famously launched a Communist terror campaign against private railroad executives once.
