It was pretty well established at the end of WW2 that the German military fought a mostly clean war (with some glaring exceptions in the east but considering the brutality of their opponents there, no surprise). Notice that only now, decades after the fact, when nearly everyone involved is dead, “new scholarship” has been “deconstructing the myth of the ‘good Wehrmacht’”. By comparision, it was established and known, during and after the war and up to the present day, that the Japanese military was horrifically brutal in its treatment of enemy troops, prisoners, civilians, women, children, everyone.
IIRC, The Japanese commander of a portion of occupied China spiked cigarettes manufactured there with opium to create a population of addicts. Much easier to control them and provided revenue for the corrupt commander.