The Socialist Republic is obviously communist and occupies the least productive lands so famine and industry lacking is going to be typical.
The largest harbours and shipyards are all in the South so without massive support a Naval blackade would work. Korea and China will likely not want too much to do with the war but would avoid Communist victory through favourable trade practices. As far as the fighting goes the battles would be vicious due to the martial nature of Japanese culture in an historical sense.