By Martin Baccardax

Japan closed out the second quarter with a triple set of historic events this week, including a massive 38% gain for the NIKKEI 225 and the highest interest rates in more than thirty years following Bank of Japan tightening in June.

The third of the three, however, is likely to cause the largest upheaval in global markets and could rattle U.S. stocks over the coming weeks, as authorities in both Tokyo and Washington search for a solution to what is quickly becoming a systemic issue for the world's fourth-largest economy.

Japan's yen fell to the lowest levels against the U.S. dollar in more than 4 decades on Tuesday, changing hands at 162.41 and extending its second-quarter decline to around 4%. The dollar itself, meanwhile, has gained around 5.3% against a basket of its global peers since late January.

Those moves have defied both the Bank of Japan's hawkish tone and a record $72 billion effort from the Ministry of Finance to defend the currency's slump between the latter part of April and the final days of May, when the yen first crossed the 160 mark.

Finance Minister Satsuki Katayama has repeated her warnings on intervention this week, telling investors that Japan will "take appropriate action whenever necessary" to defend the currency, and held recent calls with U.S. Treasury Secretary Scott Bessent to ostensibly form a joint effort in arresting the yen's slide.

Investors have long borrowed cheaply in the Japanese currency and put the cash to work in higher-yielding markets, a tactic known as the yen carry trade. That has kept a steady stream of Asia-based money flowing into risk assets around the world, including U.S. stocks and commodities.

Developments here are worth watching, especially as markets approach the two year anniversary of Japan's massive yen intervention in August of 2024, which stoked not only the biggest single-day decline for Japanese stocks since 1987, but also a spike in U.S. market volatility and a three-day 6.1% slump for the S&P 500.

ING's global head of markets, Chris Turner, thinks Japan could react with a fresh round of yen buying on Friday, given the holiday-thinned markets of July 4, or wait until just before the next Japanese holiday — Marine Day — on July 20.

"Nonetheless, Japanese authorities will appreciate that intervention can only try to slow, not reverse, the current bull trend seen in the dollar against the yen," he said. "A reversal would require not only some dramatic Bank of Japan rate hikes, but also a turn in the broad dollar trend."

Turner doesn't see that happening until "much later in the year, once current Fed hawkishness has run its course."

Those conditions, it seems, could keep markets on edge for much of the summer, given that the prospect of intervention carries the threat of broad market pullbacks. But the gains seen in Japanese stocks, and their close connection to the popularity of new Prime Minister Sanae Takaichi, may prevent Japan from pulling the trigger.

Takaichi, in fact, vowed to align Bank of Japan policy with government objectives to boost growth and investment in her first "economic blueprint" on Tuesday, effectively leaving currency intervention up to the Ministry of Finance.

And for markets to consider heading into the start of a questionable third quarter.

"The yen carry trade is the global liquidity lever almost no one watches until it moves," said Michael Gayed, portfolio manager of The Free Markets ETF. "And every condition that made it dangerous in the summer of 2024, a wide rate gap, a yen at the 160 line, and a central bank that must keep tightening, is present again in the summer of 2026."

Write to Martin Baccardax at martin.baccardax@barrons.com

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