I think they have very different reasons for fearing NK's collapse. Education isn't all that big a deal - these are pretty sharp people, who will improve tremendously with proper nutrition and instruction. NK is not a garden variety basket case country - notice that Zimbabwe doesn't have working nukes or ICBM's, and has to import its weaponry. For China, NK's fall will remove a buffer state, and bring US troops all the way to the Yalu river - something they fought a war in 1950 to prevent. For SK, NK's fall could bring about a Chinese intervention and an attempt to annex North Korea - which would bring about war with China and the Chinese confiscation of SK's plants in China as well as an interruption in its lucrative trade with China.
The backlash against Japan in the postwar era has distorted Korean views about Japan, but the principal threat to Korean independence for most of Korea's history has been China rather than Japan. If it weren't for Japan's annexation of Korea in 1895, Korea would probably be a Chinese province today.
Thing is, that the Chinese view Korea as a tributary state, a country they have a kind of ambiguous claim to over-lordship, in exchange, they do business and protect the country from foreign invasion. So predictably, they would feel obligated to protect Korea at all costs.
As for the collapse of Kim Jong-Un and the rest of his dynasty, it’s iffy since they view him as a client king, in position by the amused tolerance of China, with the occasional push-back if Kim gets too aggressive. Now if the Japanese would attack NK, then of course, the Chinese might believe they are honor bound to defend NK, since NK is viewed as part of a whole Korea that would require their protection.
Throw in the fact that the Chinese hate the Japanese and then it would be a perfect diplomatic mixture for another world war.