The best I could find somewhat vaguer talk from NK in 2018 of denuclearising the "neigbouring" region...
The statement carried by the North’s official Korean Central News Agency comes as the United States and North Korea struggle over the sequencing of the denuclearization that Washington wants and the removal of international sanctions desired by Pyongyang. [...]
North Korea for decades has been pushing a concept of denuclearization that bears no resemblance to the American definition, with Pyongyang vowing to pursue nuclear development until the United States removes its troops and the nuclear umbrella defending South Korea and Japan. In Thursday’s statement, the North made clear it’s sticking to its traditional stance on denuclearization. [...]
“The United States must now recognize the accurate meaning of the denuclearization of the Korean Peninsula, and especially, must study geography,” the statement said.
“When we talk about the Korean Peninsula, it includes the territory of our republic and also the entire region of (South Korea) where the United States has placed its invasive force, including nuclear weapons. When we talk about the denuclearization of the Korean Peninsula, it means the removal of all sources of nuclear threat, not only from the South and North but also from areas neighboring the Korean Peninsula,” the statement said.
The United States removed its tactical nuclear weapons from South Korea in the 1990s. Washington and Seoul have not responded to the North Korean statement.
Given the somewhat vague language in the NK statement that includes the "areas neighboring the Korean Peninsula", I guess it's not entirely unfair to infer that NK may implicitly ask for the US to withdraw nuclear weapons and/or the "nuclear umbrella" from Japan...
The vague demands in this are are nothing new; around 2013, similar ones were quoted/paraphrased.
The opening North Korean bids are very high. The National Defense Commission statement seeks: [...]
A “withdrawal of nuclear war means” from around the peninsula. This demand is at one level virtually impossible to meet given the dual nuclear and conventional capabilities of the US bomber and submarine fleets. But on the other hand, it is vague enough so that it could probably be finessed.