"Men Behind The Sun" is based on the true story of the prison camp, Manchu 731, where people were subjected to tremendous horrors.
The film opens with the passage "Friendship is friendship; history is history." Mou said of the quote, "that's the argument [I had] with the [Chinese] government, because the government says 'no, we have a friendship with the Japanese', I said 'well, you can talk about your friendship, I am talking about history.'"[1]
The film follows a group of Japanese boys who have been conscripted into the Youth Corps. They are assigned to the Kwangtung Army, and are brought to one of the facilities serving Unit 731, which is headed by Shiro Ishii. Soon, they are introduced to the experiments going on at the facility, for which they feel revulsion. The purpose of the experiments is to find a highly contagious strain of bubonic plague, to be used as a last-ditch weapon against the Chinese population.