Rodong's are on mobile launcher,and Taepodong is launched on the fixed surface launcher. We also know where these missiles are made. Key production facilities are near Pyongyang. They can be all taken down by air strikes or conventional missile attacks.
The facilities need to be not "taken down" but destroyed beyond any salvage or repair. Conventional attack to obliterate a large plant would need quite a lot.
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.