The Japanese routinely would rescue Allied sailors in order to interrogate them and then execute them. Their atrocities in China were so bad that even the Nazi Attache in Nanking tried to intervene . After the Doolittle raid the Imperial Army went mad in China and slaughtered thousands, destroying entire villages. Their military deserved nothing more than to be wiped out to a man.
Almost 50 years prior to WWII the Japanese military in the Russo-Japanese War & WWI were an honorable foe. Their treatment of Russian POWs was exemplary as was the few German & Austro-Hungarian POWs they had from WWI. There was international praise on the Japanese military’s behavior. I’ve never read a convincing historical study as to why this changed. Most I’ve read blame it on the racist attitudes of the West particularly at the post-WWI disarmament conferences where Japan was not treated as an equal ally. Maybe so, it still seems to me a too easy of an explanation. I find it inadequate.