Some thoughts at the Diplomat on Japan’s view of the legality of US strikes against North Korea:
As we know, the United States has a novel interpretation of the right of self-defense; essentially, it believes that the long-term threat posed by North Korea can justify an attack, even absent any direct, specific, immediate threat. How does Japan view this “self-defense” justification for giving North Korea a “bloody nose?”
Even with recent diplomacy, the situation in Northeast Asia remains tense. The Trump-Kim summit meeting may happen; less likely, it might produce results which would significantly decrease regional tensions. Similarly, Shinzo Abe’s apparent openness to meeting Kim could make put the bilateral DPRK-Japan relationship onto stronger footing. But if the summit fails, the “bloody nose” option may find its way back onto the menu. Indeed, some have argued that Trump will use the failure of the negotiations as pretext for a more aggressive approach.