(from ebookjapan):

During the Cold War at the end of the 20th century, the Soviet Union suddenly invaded Hokkaido. Motofumi Kobayashi, a leading war mangaka, realistically depicts the "if" of history!　

The Soviet coup triggers World War III! The Soviet Far East Army decides to land on Hokkaido to prevent U.S. forces in the Far East from moving toward the European theater of war. And so begins the epic battle between the Soviet Armored Division and the Self-Defense Forces!