Write an interesting, riveting alternate history scenario in the form of a lengthy, descriptive history book chapter in which the 1987 June Struggle in the Republic of Korea in South Korea is unable to be suppressed by the Republic of Korea Armed Forces [ROKAF] and quickly snowballs into a revolution against the authoritarian dictatorship of the Fifth Republic of Korea, spreading even into the Soviet satellite of the Democratic People's Republic of Korea [DPRK] in North Korea and toppling the regime of Kim Il-Sung in North Korea and the military junta regime of General Chun Doo-hwan and Chun Doo-hwan's successor,  Roh Tae-woo in South Korea. 
After the fall of the republican dictatorships occupying the Korean peninsula, the Korean pro-democracy movement decides to restore the Daehan Jeguk/Taehan Jeguk [Korean Empire], which had initially ruled Korea from 1897 to 1910 as the government and administration of a united Korean peninsula free from American, Chinese and Soviet influence. Some of the more radical members of the Korean democracy movement are not satisfied with this however, as in their mind republicanism is viewed with corruption and dictatorship, and stage a 'referendum' that essentially has Japan reannex Korea as a region of the Japanese state, with the House of Yamato, the Japanese imperial family taking over the imperial positions once filled by the Yi dynasty in the Joeson kingdom and later the Daehan Jeguk/Taehan Jeguk, in exchange for Japan agreeing to help prevent Juche, Illmism and supporters of the now deposed military dictatorship in South Korea, from regaining power in the Korean peninsula. 
Sometime later, Chiang-Ching-kuo, son of infamous dictator Chiang Kai Shek and current leader of the Republic of China in exile on Taiwan, is assassinated by an unknown gunman while giving a speech in Taipei and the local pro-democracy movement, sick and tired of the brutal regime of the Chiangs and wishing for change, quickly seizes control of Taiwan from the distracted Kuomingtang and ROC government. The Taiwanese pro-democracy rebels hold a referendum on the status of Taiwan which sees the ROC dissolved and Taiwan return to Japanese rule as the Formosa region.