Read the Franks book years ago and recently re-read it. Highly recommended.
Japan set the rule for that war and the rule was no mercy for anyone considered an opponent.
POWs - no mercy as they were tortured, beheaded, enslaved and worked/starved to death.
Battlefield wounded - no mercy as they were bayonetted.
Unarmed corpsman and medics with red crosses on their helmets - no mercy and use the red cross as a target. Kill the medical help and kill those who could have been helped.
Wounded soldiers in hospital beds - no mercy as they were bayonetted.
Western civilian internees - no mercy as they were enslaved and worked/starved to death.
Asian civilians, Chinese, etc. - no mercy as they were slaughtered in the millions.
The US played by Japan’s rule and had no mercy. Too bad for Japan, but they had it coming.
The funny thing is, they make such good cameras.