In World War II, both the Japanese and the Americans used propaganda to depict one another in extremely negative ways. This is, of course, quite normal during a war.
In Japanese propaganda, Americans (and to some degree other Westerners) were portrayed in a number of negative ways. They were portrayed as arrogant colonizers who felt that they had the right to lord it over the Asians. They were portrayed as soft and effete, without the sort of bravery and devotion to their country that Japanese felt they themselves had. They were portrayed as being materialistic and lacking in moral values. Basically, the major Japanese way of portraying Americans was to say that they lacked all of the sorts of character traits that Japanese admired.
In American propaganda, Japanese were generally portrayed as animalistic, cruel, and in essence subhuman. Many propaganda images of Japanese people were caricatures of Oriental facial features, often with animalistic aspects added. The Japanese were portrayed as cruel (particularly because of atrocities that they actually did carry out) and sneaky. They were depicted as savage little things that only succeeded in war through underhanded and cruel actions.
These depictions were meant to stir up hatred for the other side.