The Imperial Japanese army was horrifyingly cruel in World War II. Whenever the Imperial Army conquered a country, certain groups of Japanese individuals, usually young immature men, would come and bring terror to the towns and farms they occupied. Entire families were bayoneted, raped, and killed mass. It is estimated that over 10 million people were murdered in massacres across Asia by individuals of the Imperial Army.
In the Phillipines, IJA soldiers entered in a hotel full of refuges and bayoneted infants of mothers pleading mercy and raped women seeking refuge. At least 20 individual soldiers raped a young girl before slicing her breasts off after which an Imperial soldier placed her mutilated breasts on his chest to mimic a woman while the other soldiers laughed. The Soldiers then doused the young girl and two other women who were raped to death in gasoline and set them all on fire and this hotel was full of mainly German refuges, who were considered friends of the Japanese empire.
Life for POWS was horrible under IJA rule. There have been many well-documented reports of Imperial soldiers dining on their enemies. Supplies were running low throughout the Pacific Theatre, so the Imperial began selecting prisoners at work camps to consume. In some cases, soldiers cut flesh from still-living prisoners. Hunger makes people go mad, no matter what race or ethnicity.
Of course, history is not black and white. There were a lot of good Japanese soldiers who helped Chinese civilians run away from immoral individuals who were killing or kidnapping people. Other good Japanese soldiers tried to help ease the “comfort women” who were basically young girls who were told they were going to be conscripted to make army uniforms before being betrayed and sent to the front to be raped by certain individuals of the imperial army.
The reason the IJA was so cruel was not because they were ethnically Japanese (I know a lot of Japanese people and generally they're a very nice and polite group of people) but because of the government spreading nationalistic racial superiority propaganda everywhere making soldiers think they were entitled to war crimes. That's why nationalistic propaganda is so evil. It leads men to becoming animals and to treat other people with the most unorthodox ways ever.