Look, my country has been occupied by Nazis and i have read extensively books about the Nazi crimes in my country or in other countries.
I can very confidently say that the enormities commited by Nazis werent even close to the enormities commited by the Japanese, both in scale and in brutality. Just think that Himmler invented gas camps because he was worried about the mental health of the soldiers who were executing with a gun. Being killed by a gun in Japanese occupied areas should be considered as a merciful killing if anything.
We also cant talk about isolated incidents because it happened in massive scale in every country that Japan occupied.
Just what are the social and cultural reasons for such gigantic brutality? Was the Japanese society ultra strict and violent? Was it glorifying torment? What happened?
I'm not entirely sure that you can say the crimes by the Nazis "weren't even close" to those of the Japanese. The Nazi crimes and Japanese crimes were very different in origin: Many Nazi crimes were ultimately government sanctioned and instituted by government officials, while the Japanese crimes were primarily the result of an utter lack of government control over the actions of troops on the ground. I talk about this a bit here.