Trilateral ties may be unshakeable, but good luck trying to get North Korea to denuclearize because that is pretty much a fantasy as this point:

The top diplomats of South Korea, the United States and Japan held their first meeting since the launch of the new Trump administration, reaffirming their “unshakable trilateral partnership.”
Foreign Minister Cho Tae-yul and his American and Japanese counterparts Marco Rubio and Takeshi Iwaya held talks on Saturday on the sidelines of the Munich Security Conference in Germany.
According to Seoul’s Foreign Ministry, the top diplomats discussed ways to enhance trilateral cooperation, responses to North Korea issues including its nuclear weapons, regional situations, and ways to expand economic cooperation.
In a joint statement, the three sides reaffirmed their resolute commitment to the complete denuclearization of North Korea.
You can read more at the link.