I will make a prediction about Japan:
Stage One: In next 5 years the atrocities of imperial Japanese left in Aisa will be widely known to global community (most noticeable in bottom-up social media), inevitably.
Stage Two: Japanese young people used to think China is the one that should be isolated by the "world", but after communication and verification they find the west liberal young people are the ones opposing Japan most.
Stage Three: Japanese younger generation is neither the war criminals nor benefit from honoring the war. Then many Japanese young people realize it is better make a cut to their vorfathers who committed the horrible things, preventing shame coming from international community towards them. Japanese rightwing propaganda becomes unpopular.
Stage Four: United State still wishes Japanese rightwing to buffer China and a bad terms between the two countries benefit US interests. Thus US will continue supporting the rightwing elites stronger. Thus there will be stronger inner conflicts within Japan.
Therefore:
1. I think Japanese leftwing should work most hard with the western public, not China or Korea. Japanese public gives to shit on what Chinese thinks of them, but concerns how the global north view Japan.
2. I use the experience how German society used to remove German rightwing in population predict Japan: first make cut, second pass on the memory.
3. Chinese and Japanese won't make much agreement on this matter through talk, most likely a waste of time: Chinese talk about history and ethics, Japanese think the Chinese are with first political tricks. Let the international community do the pressure, and it likely has surprising good effects.
4. The Chinese govt knows better and better how to moblize international community to serve its strategic goals as it further develops. I only see more people from the west get closer to China, within 5 years the change is very evident.
5. Rightwing Japanese elite focus on doing two kinds of propaganda: Strongly connecting Japanese young people to their vorfathers thus "making a cut" never happens; keeping politically endorsing the western countries to prevent "pressure from the west base" from happening.
Those conclusions come from a pure third-party, non-emotional analysis.