The prime minister's advisory panel on national security has recommended a reconsideration of Japan's adherence to the so-called three nonnuclear principles. The panel specifically urged that the third principle, the prohibition on the introduction of nuclear weapons into Japan (which forbids not only the stationing of weapons in Japan, but even the transit of weapons through Japan), be relaxed in order to permit the U.S. greater freedom in deploying nuclear weapons in Japanese territory.
This is a bad idea for many reasons, but for one it would be inconsistent with the Constitution.
As is well known, Article 9, paragraph 1 of the Constitution renounces war and the threat or use of force as sovereign rights of the nation, while paragraph two prohibits the maintenance of armed forces or other war potential, and denies to Japan the right of belligerency. The long established official understanding of paragraph 1 is that Japan can only use the minimum military force necessary for its individual self-defense. It cannot use or threaten the use of armed force for collective self-defense, or for U.N. collective security operations.