Look, the google Japanese doesn't come out so well. But well, I'll try to respond.
During the Meiji period, Japan was looking out for itself. That was the kind of world it was. It is important to keep in mind that the Europeans were not a single entity. They competed with each other. Everyone was competing with everyone. The strong made colonies, the weak became colonies. In Asia, Japan competed with the US (Philippines), Russia (Korea, North East China), France (Vietnam), Great Britain (Hong Kong, Singapore, Malaysia, Burma, and India), and the Netherlands (Indonesia). That's a scary place.
After WW1, China was still not unified, only real briefly under Yuan Shikai. Although he backed stapped Sun Yat-sen. In order to fight Yuan Shikai, Sun Yat-sen need outside support, and no one would give him major help, so he turned to the Soviet Union for help. So the Soviet Union got their fingers into China by supporting him. And part of that support agreement was to let in the 1st generation of Chinese communist such as Mao and Deng. Sun Yat-sen soon died, and his follower Chiang Kai-shek took over the KMT and shortly after a trip in the SU and working with the Chinese Communist, he reasoned them to be a cancer to China. So he became very much against them.
Anyway, the warlord wars went underway, Japan backed the clique that was in North East China. But that clique suffered a major defeat, and it's economy went bad by 1930. While the Japanese were south in Korea. Everyone seems to forget that the Soviets were north and east. And it was the Soviets that built the railway line in North East China. So when that clique became weak, it's rather reasonable to expect that the Soviets might fill in if the Japanese had not invaded. There was no other Chinese clique strong enough to fill in North East China. So the Japanese went in, well the Japanese Army that is, Tokyo government was still against it.
When all these factors, and many more (I could go on) are considered, I think a view comes out to not take the history so personally. Of course for relations to improve, Japan should still apologize since they did invaded, regardless of the geopolitical situation that was going on. But these days, I think it is the new geopolitical situation that keeps people in China thinking of not letting go of the past.