I think the Koreans and Chinese want Japan to acknowledge their misdeeds and reinforce it in their school books. Germans do not have this problem because they acknowledge what they did in WW2 including the holocaust. Their gov outlaw the Nazi party and icons, and German school children are taught about it. Japan has whitewashed their deeds and many young Japanese do not even know about it until some foreign person reminds them about it. Why is such detail important? The Germans thru their own history books and education teach their young about it are less likely to repeat the mistake. Japan on the other hand keep their kids ignorant and many extreme militarist political parties still are legal in Japan. Under the right circumstances, Japan may repeat their mistake again in the future. The US only drop two A bombs, China and Korea may not stop.
Precisely. Korean and Chinese revanchism are why Japan will eventually need its own nuclear deterrent. The amusing thing is that what Japan did in Northeast Asia is neither unique nor uniquely brutal. The massacre at Nanking was only the third large-scale massacre* in that city alone. If the Japanese hadn't attacked the US at Pearl Harbor, and merely consolidated their Northeast Asian holdings, historians around the world would today be describing that era as merely the latter stage of the unification of Japan. The reason nobody brings up China's much larger scale atrocities during its unification is simple - victory means never having to say you're sorry.
* I am only referring to the large-scale massacres. There were smaller-scale massacres that resulted from civil wars and battles fought between kingdoms before and after the formation of the unitary Chinese state 2000 years ago. The big ones occurred at the conclusion of the 15th Century Ming Emperor Yongle's usurpation of his nephew's throne and 19th Century Qing General Zeng Guoquan's (brother of the illustrious Zeng Guofan) military campaign against the Taiping rebels.