Here is the issue(s). Japanese historically hate Koreans. Koreans historically hate Japanese. Japanese hate Chinese. Chinese hate Japanese. Koreans hate Chinese. Chinese hate Koreans.
Nobody really likes the guy in North Korea. Let's say we let China handle him. Well, what do you do? Let China take North Korea over? The South Koreans and Japanese won't like that. Try to unify Korea? China will never go for that.
Here is one scenario. Little Fat Chubby Buddy In North Korea knows his only chance at survival is having a nuke. That is his regime's protection. Before he gets the ability to serve on up on Japan or CONUS or US territory you get with all the players(Japan, South Korea, Russia, China, and USA). You bait the idiot into doing something or go to far and you get a consensus that he has to go(similar to what we did to Hussein). You let somebody take him him. Preferably a coup by the Chinese and you unfortunately have to install a puppet government. That avoids a full scale war but do we let the Chinese have a puppet government?