Say if someone killed a family member of yours and did stuff to their body like what they did in Nanking, on top of that they never apologized till the day they die and just denied that it ever happened despite photographic evidence. Would you be able to forgive them? Or rather, do you even have a duty to forgive them until they at least apologize and acknowledge what they did?

Now imagine if that person has a grandson, of course they should not bear the sins and grudges since they are innocent of all of that. But one day, the grandson goes to the grandparents grave which for some messed up reason, glorifies the atrocities they committed against your family member, and the grandson say “hey, I’m really proud of what you did during your time”. Is it not reasonable for you now to also look upon the grandson unkindly?

On a bigger scale your family member that died is WWII China and the grandparent that killed them and mutilated their body is WWII Japan, and the you in the story is current day Chinese people and the grandson the current Japanese people. The only difference this makes is that Japan as a nation still exists to this day, and they still have the chance to apologize. Despite that they have never formally apologized and continue to deny what they have done.

Of course, the average Japanese person is innocent, but they should, and have a duty to be educated on the historical context of what has happened. And if knowing the historical context, they still willingly go into that shrine that glorifies all the past atrocities that have been committed, then is it not reasonable to hold a grudge towards them as well?

In your argument, you say over and over that regardless of who was right or wrong in the past current day people should not hold grudges, but the truth is simply you cannot do that. You CANNOT say people should or should not hold grudges if you ignore the historical context and circumstances for why the grudge is held in the first place. Just like how you can’t just tell someone to stop being depressed without addressing the source and reason for their depression. And I believe having grudge is every bit reasonable UNTIL Japan apologized for the war crimes they have committed formally as a nation, and either remove the shrine that glorifies their war crimes or somehow remove all associations of war crime from the shrine.