Japan will apologize when everyone who could have been involved and their children are dead.

Face is very important.

The issue is Japan has apologized to both China and S.Korea over and over again for the last 30 years but it was never in a way that was "acceptable".

It either was considered incensed or did not come from the Royal Family, etc.

I would say that Japan did some nasty things during the war, but at the same time there is documented evidence that many Koreans women did volunteer to be "comfort women", some were forced into it by Korean or Chinese pimps, some were forced by the Japanese military it is quite complex.

As far as the "war crimes" no one argues that Japan killed innocent people in Nanjing or Shanghai...in every war innocent people get killed.

We firebombed Dresden and drop nukes on nonmilitary targets for God's sake. We dropped nukes on the centers of Nagasaki and Hiroshima, which are not in any way military targets or even major areas of production. We did it to make a point.

Japanese level Nanjing to make a point. They were trying to make the Chinese surrender by intimidating the Guo Ming Dong (KMT). The issue is not "if" but how many. The Japanese figure is obviously too low and the Chinese figure is too high.

Also you have to remember that this issue is political. It is not about "justice" in and of itself. China has a lot of domestic issues from income inequality, Taiwan, and corruption. China needs a nationalist rallying point to help stabilize things. Japan is that punching bag. If you ever watch any protest in China, the one's allowed in the major cities are all scripted by the party and allowed to go so far. Those that are not scripted never make it to the press (there are thousands of protest and even riots yearly in Japan in rural areas you rarely ever hear about). China is using this situation. Way back when China made normal relations with Japan they made a deal with Japan to "let the past go" in return for FDI, low interest loans, etc. Japan agreed, however China won't let the issue down because they realize they can use it to get more and more concessions. This pisses Japanese people off.

Korea is more complicated. There are pro-Japanese and anti-Japanese factions in Japan before Japan annexed Korea. There were Koreans begging Japan to invade and modernize it, anyone aware of Korean history at the time knows, this and most Koreans will admit it. In fact one of the greatest leaders of Korea, Park, who really did the most to modernize Korea spoke fluent Japanese, often read Japanese books and watched Japanese movies, was educated in Tokyo in the military academy and many people after S.Korean independence were similar to him. The Korean elite were Japanized. Remember Korea was part of Japan for 50 years, and so was Taiwan (same there, but the Taiwanese, on average, do not hate the Japanese because they were not brutalized. Why? Because they gave up and submitted. So they got a lot of "goodies" and not a lot of hate, Koreans never stopped fighting against Japanese rule so the Japanese treated them quite harshly. This is classic Confucianism, you have to bow to your nation and your ruler. If you don't submit you are "the nail that has not been hammered down or the blade of grass that has not been cut". In any case the Korean elite realized that power of nationalism (part of that was hating Japan and blaming them for every single thing wrong in Korea) to help keep S.Korea together and focused on the goal of "Korean development and nationalism" part of which was to become "better than" Japan.

You also have to remember that for most of its history, Korea and China were superior to Japan in every metric and considered the Japanese barbarians. Japan industrialized first and became the dominant Asian power in a 50 years period. They became so far they did what no other Asians did, ran the white people out of Asia. This in and of itself brought resentment from Koreans and Chinese that these “former barbaric Japanese” were lording over them, who were culturally superior.

All these things are at play.

What I believe is Japan will apologize (for what they did and for what they didn’t do) when they have to. Right now they don’t have to. They are still the strongest nation in Asia by far, but as China becomes more and more powerful, in the next 50 years due to geo-politics they will because the Chinese will have enough leverage to force their hand, but by that time everyone involved will in WWII and their kids will be dead.