Japan and the United States have confirmed a rare, coordinated intervention to buy yen and halt the Japanese currency's slide to 40-year lows, with both governments signalling they are prepared to act again if necessary. Japan's Finance Ministry announced on Monday that Friday's joint action with the US Treasury Department "countered excessive volatility and disorderly movements in the Japanese yen in recent months," adding that it "will not hesitate to conduct further joint intervention." US Treasury Secretary Scott Bessent echoed that commitment, saying Washington "will not hesitate to participate in further joint intervention" and expressing strong support for Japan's efforts to "correct the substantial undervaluation of the yen."

The intervention is the first coordinated currency action between the two countries since 2011, when they jointly moved to weaken the yen following the devastating earthquake and tsunami that struck eastern Japan. This time the direction is reversed: both governments are buying yen to push its value up. US President Donald Trump framed the move in diplomatic terms, telling reporters on Sunday, "They have a weakening yen, and they wanted a little bit of help. And we're always there for Japan." Japan's top currency diplomat, Atsushi Mimura, called the joint action "the culmination of Japan's alliance with the United States." In a further sign of regional coordination, South Korea also intervened to support its own currency, the won, on Thursday.

The yen has been weakening for structural reasons that a single intervention is unlikely to resolve. Japan's central bank interest rates remain far below those of other major economies — the Bank of Japan raised its benchmark rate to 1 percent in June, its highest since 1995, while the US Federal Reserve's rate sits between 3.50 and 3.75 percent. This wide gap makes the yen less attractive to international investors. Japan also faces long-term headwinds including a shrinking working-age population, low productivity, and heavy reliance on energy imports priced in US dollars — costs that have risen sharply amid conflict in the Middle East. Prior solo interventions by Tokyo in April and May produced only brief rebounds, and the June rate hike provided little lasting relief. Bank of Japan data suggests Japan may have spent as much as $58.97 billion buying yen on Thursday alone, before Friday's confirmed joint action.

Market reaction was swift but mixed. The yen gained as much as 1.4 percent, reaching a nearly three-month high of 155.20 per dollar, while Tokyo's Nikkei share index fell sharply as a stronger yen weighs on Japan's export-oriented companies. Analysts note that the "announcement effect" of joint intervention carries more weight than unilateral action, but caution that underlying pressures remain. "The fundamentals driving yen weakness haven't changed, so we likely won't see one-sided yen rises from this intervention," said Tsuyoshi Ueno, a senior economist at NLI Research Institute. Bessent also indicated that the US Federal Reserve's dollar-liquidity facility — originally created during the Covid-19 pandemic to allow countries to raise dollars without selling US Treasuries — could be expanded in the coming months, providing Japan with an additional financial backstop for future interventions.