From what I know,Japan's ability to carry out long range strike missions is pretty limited.Their main strike force is still based on F-4s & their newer,but shorter range F-2s.Their F-15Js are not known to have (officially) any PGM capability.Unless they can do stand-off strikes,any likely attack on North Korea by them alone would be very bloody.That being said,their JMSDF can starve the living daylights out of North Korea.