Can you give some examples of Korean literature portraying Chinese as villains? The time period you're talking about would have been during the Japanese colonial period. Korean literature and culture was being suppressed and/or co-opted/directed by the Japanese authorities, so if you could give some examples, I think it'd be easier to answer.

As far as 1931, there were two incidents - the Wanpaoshan Incident and the Mukden Incident. The Wanpaoshan Incident involved some Koreans (who were Japanese subjects at the time) living in Manchuria who rented some farmland. They started digging a canal through some other land that they didn't own, the local Chinese got upset, and there was a clash. The Japanese consulate came out to protect the Koreans and that was about the end of the whole thing.

BUT, back in Korea, the Japanese and Korean (under Japanese control/rules/influence) papers sensationalized the whole situation and violence broke out against Chinese living in Incheon and Pyongyang (as well as the rest of Korea, but those were the main locations). Then, in September, the Mukden Incident occurred (a Japanese false flag/sabotage mission to justify "intervention" in China) and the Japanese began their invasion of Manchuria and conquest of China.

So I would say that this all ties in to the mutual distrust between China and Japan that had been going on for quite some time. China and Japan had an agreement that if either one of them were to enter Korea, they would notify the other. In 1894, the Tonghak Rebellion occurred in Korea and the Joseon government requested help from the Chinese, who in turn sent help but did not notify the Japanese. That was the start of the First Sino-Japanese War. A short time later, the Russians, building a train line through Manchuria and seeking a yearlong ice-free port on the Yellow Sea, started to worry the Japanese. The Russians had decent ties with the Koreans (King Gojong and his son hid out at the Russian legation in Seoul for two years after the king's wife was murdered by Japanese assassins) and a few years later, the Japanese went to war with the Russians. Feeling like the Koreans could not be trusted/manage themselves in a way that the Japanese found acceptable, they annexed Korea in 1910 as a way to 1) expand their empire/get a foothold on the mainland and 2) to act as a buffer between themselves and China.

Any negativity seen in media/culture/literature towards the Chinese would have come as part of the Japanese campaign to build up support domestically (and, to a lesser extent, internationally) for their empire expansion.