Imperial Japan was the regime that led Japan during the dark chapters of World War II, they were considered to be especially vicious towards conquered civilians as well as their prisoners of war - stemming from a fanatical belief in Imperial Japan that to be captured by one's enemies was a disgrace and thus prisoners were to be treated as cruelly as possible.
Imperial Japan were also infamous for their fanatical willingness to die and their reliance on fierce ambush tactics, such as in the raid that devastated Pearl Harbor. They were responsible for massive destruction and the brutal murdering of tens of millions across East Asia during the Second World War. They also showed an incredibly racist attitude towards non-Japanese Asians, which served as the primary reason behind why they killed so many of them.