Russia had the largest number of casualties during WW2, and Russia had taken many Japanese prisoners. So, why didn't Russia receive a reparation from Japan to help boost Russia's economy after the war?
Japan agreed to pay war reparations of 1.3 trillion yen. The Japanese GDP in 1952 was 6,217 billion yen. So the reparation was 20.91% of the Japanese GDP. The Japanese GDP in 2011 was equivalent to $5.869 trillion 2011 USD. So the reparations were equivalent to 1,224 billion 2011 USD. This was all proposed at the Treaty of San Francisco in 1952. The soviet Union, however, disagreed with many points:
They also objected over other minor points. In the end, the Soviet Union refused to sign along with Czechoslovakia and Poland.
It was not until October 19, 1956, that Japan and the Soviet Union signed a Joint Declaration ending the war and reestablishing diplomatic relations.
Land-starved Japan ceding territory to the Soviet Union, a nation that ruled a landmass larger than some continents with only twice Japan's population, had to hurt, and bad... and still hurts to this day.