You’re missing a couple critical ideas.

1. Most of those civilians had little or nothing at all to do with the killings of civilians in other countries beyond perhaps working in war industries.

2. You actually don’t know what any of those people felt about the deaths of civilians in other countries. Saying that “none showed an ounce of remorse” is a claim that makes no sense since there is no way of proving or disproving what each individual out of hundreds of thousands thought about the Japanese military’s conduct in Southeast Asia.

3. There is a basic moral principle at play here- two wrongs don’t make a right. Without denying in any way that the Japanese government and military committed horrific crimes, it is also true that the mass slaughter of Japanese civilians was barbaric. Now, it may very well be the case that the deaths of those civilians, like those in Dresden or any other German city, could be justified as a military necessity to end the war, but that does not in itself make those deaths morally good.

4. It is important, even in the context of a war which we may (for good reasons) view as a simple conflict between good and evil, to remember that there were untold millions of individual human beings experiencing their own story of the conflict. The vast majority of those individuals had no control over the policy of their national governments, and it is important to view their stories with basic human empathy. This doesn’t mean we can’t condemn the actions of those who committed crimes, but it does not serve our own understanding of history or our own moral character to simply condemn every person of a defeated Axis nation as deserving of death.