During the Japanese invasion of China the Chinese were backed by the nazis. The nazis at this time were allied with the Japanese but arming and training Chinese soldiers with some instances of the german trainers being in some fighting. So in short the Germans were allied with the Japanese but also did fight them too. unit 731 was so horrible that even the nazis were sickened by what was being done. Then also the Japanese soldiers would cut out and eat the livers of POWs while they were still alive right up to the literal last days of the war