On Shoji's recommendation, Yoshimura joined Unit 731 in Harbin in 1938 as a technician to work in the newly established frostbite laboratory where he stayed until the end of the war in 1945.

Unit 731 ran an extensive facility there to develop biological warfare agents and conduct related research that involved experimentation on live humans.

It was part of the Epidemic Prevention and Water Purification Department, a branch of the Imperial Japanese Army that conducted combat-relevant scientific research across the battle grounds of the Pacific War and ran several labs across the occupied Chinese territories.

[1] Yoshimura later ran his own frostbite experiments at the Harbin lab where prisoners of war, criminals, and civilians from nearby villages were used as test subjects.

[3] The claim that Japan had conducted large-scale experimentation on living human beings during World War II was disregarded by the West as communist propaganda until the 1980s.