Every people is only human!
There are gravediggers, war criminals, but also idealists in each nations armed forces.
It would be wrong to claim or accuse any nation's soldiers or even people generally as evil, uncivilized etc.
Neither Chinese, Koreans nor Japanese did pulling out the corpses out of someone graves as a national behaviour. It might happen in some private cases but it is not acceptable to do this, even if it is a grave of your enemy.
War is never a good thing and the result is usually causing only more suffrage and hatred.
Every nation needs a competent and capable military to protect the country and its people but must not be abused by political power struggles and imperialistic plannings.
As for the bones. There were at least 3.2 million Chinese soliders who lost their lives from 1937 to 1945 and around 1.1 million Japanese soldiers on Chinese soil. Some (I guess the high ranking officers) might be transported back to Japan early, while many were just left behind on the battlefield. After the war was over most corpses were just burnt, so no matter they were Chinese or Japanese soldiers, they turned into ashes.