China's grudge is attributed to its defeat by Japan in the Sino-Japanese War at the end of the 19th century, and various events which occurred during WWII, especially the Rape of Nanking.

At the time of the Sino-Japanese War, China's Qing government was in its early stages of deterioration, and had recently undergone its 'century of humiliation' by western powers seeking to open up Chinese markets to worldwide trade in the 1800s. Japan on the other hand following it's encounter with American warship had quickly modernized during the Meiji period and was easily able to force concessions out of China in the Treaty of Shimonoseki.

I only have personal experience with hatred between these two people, so take my answer with a grain of salt, I doubt it is like this all over China.

TL;DR In my experience with a Manchurian family, the remembrance of the past has left a scorching hatred towards the Japaneses and their soldiers.

I am very close to a family that has recently immigrated from southern Manchuria. They are nice enough and are doing the best they can to assimilate and live the American Dream, but what sets them apart from other immigrant families I've seen is their deeply set hatred. In the older generation specifically, anything, and I mean anything, that is the slightest related to Japan will set them on a tangent.

I was watching the news with them and something about North Korea launching missiles over Japan's islands was being reported on. This made the great grandfather (who grew up under Japanese occupation) talk about how it would be doing the world a favor to brutally kill ever person on that island. He then went on to talk about all the things they deserve for what they did in Manchuria when he was a boy.

He has shoved the idea that Japanese are scum into his children, and in turn his grandchildren, so the sickness of hatred has only been spreading in their family.

Couple that with the already numerous historical grievances between the two people (most notably the occupation during WW2) and there is most likely going to be some animosity towards Japan form the Chinese people on a large scale.

I'm unfamiliar about how the Japanese feel towards the Chinese, but my grandfather was friends with a Japanese war veteran who thought of the Chinese as the lowest form of human.

I just want to remind anyone that read through this that much of this is taken purely from personal experience and connections from documented issues between the two lands.

If I've made any glaring errors or somebody can prove that this is a very rare case, I'd be happy to change some things to better fit with what can be cited.