The Japan Times reported May 9 that "Japan hopes to mediate between U.S. and Iran to rescue 2015 deal." This would be a miscalculation on the part of Tokyo.
Japan has been one of America's staunchest and most loyal allies. Tokyo supports most of Washington's diplomatic efforts, provides generous host nation support for U.S. forces in Japan and consistently seeks ways to enhance the Japan-U.S. alliance, if at a cautious pace. This trend manifested itself most recently at the "two-plus-two" talks between U.S. and Japanese foreign and defense ministers, who agreed to extend the bilateral alliance cooperation in the field of cyberspace.
However, at the risk of stating the obvious, Japan's national interests do not coincide completely with those of the United States. Over the years, to maintain strong ties with its only ally, Tokyo has acted with considerable restraint to avoid any breaches with Washington. That said, Japan has over the years quietly pursued foreign and security policy differentiation from the U.S. on the margins. This may be explained in part as the natural pursuit of Japan's national interests. At the same time, it may represent at some level an expression of frustration among Japan's policymakers that Japan's foreign and security policy is constrained by Tokyo's need to maintain harmony with Washington.