"Mercurial" could also be Trump codespeak
indicating that Kim is a messenger (e.g.
Roman god Mercury == Greek god Hermes,
messenger of the gods).
There's a old crumb saying that Kim is not the
person in charge of North Korea.
Don't know if that is still true after POTUS
"cut the strings".
Look for multiple meanings; don't settle on just one without considering as many possibilities as we can come up with.