Hirohito, known posthumously as Emperor Showa (29 April 1901 - 7 January 1989) was the 124th Emperor of Japan according to the traditional order of succession, beginning his reign in 1926. Under his reign, Japan become a member of the Axis, and fought the Second Sino-Japanese War and World War II. Although he symbolized Japanese evils in U.S. propaganda during the War, the Emperor cooperated with the reorganization of the Japanese state during the Allied occupation of Japan (which had surrendered unconditionally in 1945), and was found not guilty of war crimes. Hirohito was the only head of state of a major Axis partner not to be killed or overthrown in the immediate post-war period. He lived to see Japan become a highly urbanized democracy and one of the industrial and technological powerhouses of the world.
From 1945 until his death, the official story regarding Hirohito's role in the war was that he was a powerless figurehead who was not responsible for his councils' brutal actions. More recent analysis suggests that this innocent image was a morale-boosting lie created for convenience in reconciling old foes. Extant wartime documents have given the lie to any claims of imperial plausible deniability, therefore it is once again believed that Hirohito was indeed a prime mover behind Japan's worst atrocities.
After the war, Japan formed much closer economic ties with the United States. In 1965, Japan successfully tested its own explosive-metal bomb at Bikini Atoll, and demanded full diplomatic relations with the Race.
Despite his title, the Race saw Hirohito as a "false front" for those who wielded true power in Japan.
While Japan was initially able to gain substantial advantages in the Pacific throughout the war, by 1944 the fragile supply line they'd built began to collapse. With the war in Europe ending in mid-1944, the USSR turned its attention east again, and began closer cooperation with the U.S. in its war against Japan.
While Hirohito reigned over his country's gains against its enemies, as the war progressed, Japan found itself in dire straits. At the end of 1945, after the United States invaded Japan in the south, and the Soviet Union invaded from the north, Hirohito and his generals nonetheless remained publicly defiant to the bitter end, leading to Operation: Coronet. 
With Coronet underway, Hirohito attempted to flee Tokyo in a black car escorted by four tanks. On the road to Kyoto, the convoy was attacked by American Hellcats. Three tanks were destroyed immediately in the attack. The car was also disabled, and Hirohito himself was killed by two rounds from the Hellcats'.50 caliber machine guns. While the crew of the fourth tank survived, and attempted to rescue Hirohito, they were killed by U.S. troops who'd just happened to be present. One of the soldiers, Mike Sullivan, identified Hirohito.
In the short story, Hirohito (1901-1945) is killed when his train is struck by an incendiary bomb in roughly December 1945. While the U.S. still creates the state of South Japan, the story does not describe what type of government South Japan uses.