Looking at Japan's relations with North Korea after digging along on Hirono…
Check out this article from just last week on North Korea protesting Japan receiving one of the vacant permanent seats with the UN.
This line grabbed my attention "He also said sovereign nations' rights are being violated."
https://www.upi.com/Top_News/World-News/2019/02/05/North-Korea-objects-to-Japans-entry-to-UN-Security-Council/1531549382166/
Just looking back on the bits I remember from History class, could Japan have grabbed hold of some control in NK in order to secretly retaliate? I remember we basically gave the Japanese emperor an ultimatum and McArthur rewrote the Japanese constitution (forgive me if I am off a little, pulling from memory).