Okay, disclaimer here. I'm ethnically Chinese and from Singapore. My family has no love lost for Imperial Japan. Just making you aware of any biases I may have.

Furthermore, I have to add that any form of research or historiography of Japanese war crimes is a heavily politicized minefield that still, to this day, remains one of the most significant reasons causing tension between Tokyo and Beijing. Along the lines of "the victor writes the history book"

On the surface, this sounds like a decent argument. The Japanese lost the war, so the winners wanted to exploit them. However, throughout my own personal research on the topic, I haven't found any legitimate evidence supporting Japanese war crime denial; many revsionist arguments simply claim that the International Military Tribunal for the Far East (IMTFE) was a kangaroo court.

What specifically are their arguments? Well, many revisionists cite various anecdotes that claim that Chinese civilians and POWs were not mistreated outside of isolated incidents. For example, one of the most radical (and outspoken) revisionists, Higashinakano Shudo, claimed in his article "The overall picture of the Nanjing Massacre" that "seven cases of rape [were] the entire scope of the Nanjing Incident". This article was published in Nanking 1937, an attempt by several Princeton students to anthologize revisionist theories of Japanese war crimes. Pretty interesting read, actually.

Higashinakano later claimed in his 2006 book Thorough Review of the Nanjing Massacre that several prominent eyewitnesses of the Massacre were lying. He was sued in both Japanese and Chinese courts, and lost both times. Take that as you will.

I recommend James Burnham Sedgwick's 2009 paper "Memory on Trial: Constructing and Contesting the 'Rape of Nanking' at the International Military Tribunal for the Far East, 1946-1948" as a pretty solid and relatively neutral overview of both sides. It's available on JSTOR, so let me know if you want the PDF to look over.