Agano River
In the aftermath of Japan's surrender, the Soviets occupy the island of Hokkaido and the northern part of Honshu, under Fedor Tolbukhin with some Japanese Communists acting as his puppets in the new "Japanese People's Republic" (North Japan). Similarly, the U.S. establishes the "Constitutional Monarchy of Japan" (South Japan) in southern Honshu, Kyushu, and Shikoku. Hirohito's 12-year-old son Akihito becomes the new emperor, although he acts as a puppet to General Dwight D. Eisenhower, who is the one to actually run the country. The Agano River acts as the border between the two states with a demilitarized zone of three miles in either direction.