Red Sun in the East, A divided japan by me
Night of 14th August 1945, the coup attempt(Kyūjō incident) succeeded and the emperor was put on house arrest, as the government was now under military command, they refused to surrender to the allies even after getting hit by two atomic bombs.
As the war continued, the United States asked the Soviet Union for help in "Operation Downfall".The Soviets feeling mistrust from a former ally for not sharing about the atomic bomb, yet accepted United States offer, as the Soviet saw it was a chance to expand their influence in Asia.
On the 1st of September 1945, "Operation Downfall" Began, as US forces land in Kyushu, Shikoku and southern Honshu. The Soviets on the other hand invaded from the Kuril island and Hokkaido.
With the invasion and march to Tokyo was going at a steady pase, United States alongside the invasion droped three more atomic bombs on saitama, Osaka and Yokohama.
On 25th December US forces marched in the Imperial Palace in Tokyo and Japan formally surrender marking and end to the war in the Pacific.
After the war Japan was put into administration zones like Germany, Kyushu was controlled by UK, Shikoku under Republic of China and Southern Honshu under the United States, likewise North Honshu and Hokkaido was under Soviets control.
It was accepted that Japan will be divided like German, thus formed the US backed Republic of Japan in the South and the Soviet Backed Socialist People's Republic of Japan in the North.
In China due to Soviets being busy in Japan the nationalist supported by US won the Chinese civil war forming "The Republic of China" as the communists fled to Tiwan. Due to no Soviet intervention on Manchuria, the Korean Peninsula got independence under one US backed republic.
This is the basic Lore of "Red Sun in the East"