Just to add, and it’s my own fault for not specifically mentioning it earlier, I wasn’t thinking of just the Nazis. The record of Imperial Japan during WWII is as replete with horrors as Nazi Germany’s. The Rape of Nanking is well known, as is the Bataan Death March, but those were the tip of the iceberg, a lot isn’t as well known in popular modern memory. For examples, the Three Alls Policy (Kill All, Burn All, Loot All) in retribution for the Chinese Communist One Hundred Regiments Offensive
In a study published in 1996, historian Mitsuyoshi Himeta claims that the Three Alls policy, sanctioned by Emperor Hirohito himself, was both directly and indirectly responsible for the deaths of “more than 2.7 million” Chinese civilians.
Best known from the book and movie “The Bridge over the River Kwai” the Burma Railway was constructed at an enormous cost in human lives,
At least 250,000 Southeast Asian civilians were subjected to forced labour to ensure the construction of the Death Railway and more than 90,000 civilians died building it, as did around 12,000 Allied soldiers. The workers on the Thai side of the railway were Tamils, Malays, and fewer Chinese civilians from Malaya. Possibly over 345,000 died while working, with the death rate per month rivaling that of Auschwitz.
The Sook Ching was a mass killing of “anti-Japanese” elements after the fall of Singapore by the Japanese military, with “anti-Japanese” being openly interpreted to mean of Chinese ancestry, ~40,000-50,000 were murdered. While it pales in scale, when the Imperial Japanese Army took Singapore, they bayonetted the patients, doctors and nurses at the British military hospital
The British Military Hospital (now known as Alexandra Hospital) was caught between the advancing Japanese troops and the retreating British forces. It became the site of a Japanese massacre when between 150 and 200 staff and patients were killed on 14 February 1942.
Possibly one of the most forgotten massacres was the Manila massacre where at least 100,000 Philippine civilians were murdered by the Japanese.
The Americans who have penetrated into Manila have about 1000 troops, and there are several thousand Filipino soldiers under the Commonwealth Army and the organized guerrillas. Even women and children have become guerrillas. All people on the battlefield with the exception of Japanese military personnel, Japanese civilians, and special construction units will be put to death.
— Japanese order justifying the Manila massacre
And on the topic of rape as a war crime vs rape as a crime, during the Manila massacre:
Mass rapes
The Bayview Hotel was used as a designated “rape center”.[6] According to testimony at the Yamashita war crimes trial, 400 women and girls were rounded up from Manila’s wealthy Ermita district, and submitted to a selection board that picked out the 25 women who were considered most beautiful. These women and girls, many of them 12 to 14 years old, were then taken to the hotel, where Japanese enlisted men and officers took turns raping them.[7]
Despite many allied Germans holding refuge in a German club, Japanese soldiers entered in and bayoneted infants and children of mothers pleading for mercy and raped women seeking refuge. At least 20 Japanese soldiers raped a young girl before slicing her breasts off after which a Japanese soldier placed her mutilated breasts on his chest to mimic a woman while the other Japanese soldiers laughed. The Japanese then doused the young girl and two other women who were raped to death in gasoline and set them all on fire.[8]
The Japanese went on setting the entire club on fire killing many of its inhabitants. Women who were escaping out the building from the fire were caught and raped by the Japanese. 28-year-old Julia Lopez had her breasts sliced off, was raped by Japanese soldiers and had her hair set on fire. Another woman was partially decapitated after attempting to defend herself and raped by a Japanese soldier.[9]