Many Korean women were also used as comfort women.
True. Because Korea had been under Japanese control for 1-2 generations prior to the war, I tend not to think of Korea when I think of Japanese military aggression during the war itself. From a rape and sexual slavery context, of course, the Korean women were just as much victims as anyone else. Indeed, it was probably easier for the Japanese to implement a "comfort women" system in Korea than a lot of other places since they'd already had effective control of the country for many decades.
I read a book a couple of years ago about Canadian and British POWS held by the Japanese during WW2. They were captured in the fall of Hong Kong. The guards at their POW camp would regularly taunt the prisoners that Japan was going to invade Canada one day and all the men would be enslaved, and "we will rape your wives and daughters."
Of course, this type of threat is a form of psychological rape itself. The threat would have been somewhat stronger since Japan had already made good on this threat in multiple countries, even if they lacked the military resources to successfully invade all the countries they might have wanted to.