The Japanese captured over 2 million Chinese troops and guerrillas during the war. They returned less than 100 alive at the end of the war. That is a mortality rate of 99%. There are concentration camps run by the Germans who didn't have mortality rates as high as this. And the Japanese did things like...using Chinese prisoners for bayonet practice, holding a beheading contest (two Japanese officers had a race to see who could be the first to behead 100 Chinese POWs), eating body parts like human liver, and burying them alive. And this does not include the human experimentation done on Chinese (don't know if those were POWs or captured civilians) at Unit-731.