Each of the major theatres in this war have a sort of a different vibe. The stuff the japanese were doing had a flavor all its own. This wasn't state sponsored anything. It was a sort of weirdness that people have been trying to explain, japanese people, especially ever since. And you could have troops that are well behaved under a vigilant commander, and other troops that are poorly behaved under another one.
Japan's rising sun goes supernova and engulfs a huge area of Asia and the Pacific. A war without mercy begins to develop infusing the whole conflict with a savage vibe.