The yen's rescue is a confidence game

In the last days of July the yen sank to its weakest level in forty years. Two governments then did something they had not done since the Asian crisis of 1998: they bought yen together. Japan spent money at a record pace; the Federal Reserve, in an odd touch, sold euros on America's behalf. The yen jumped by several per cent within days. It is now hovering near ¥154, having rallied hard in the past week as the market has rushed in front of the central bank. The episode is being described as a rescue of a struggling ally. The truth is more transactional, and more telling about where the yen is actually headed.

Rescue by committee

Start with the incentives, because neither government was acting out of charity. Tokyo's problem was political: a yen so weak that it pushed up import prices, and with them the cost of daily life, for the administration of the prime minister, Sanae Takaichi. Washington's problem was different, and it is the part of the story most American investors will have missed. Japan is the largest foreign holder of American government debt. When the yen tumbles, Japanese authorities feel obliged to defend it by selling dollars to buy yen — and, if the pressure gets serious enough, by liquidating their American Treasuries to fund those sales. That is precisely what a free-falling yen threatened to force Tokyo to do in the spring. A big Japanese sale of American debt would push American bond yields up just as the administration was trying to talk them down.

Hence the art of the deal. Rather than let Japan dump Treasuries on the open market, Washington steered Tokyo toward the Federal Reserve's FIMA facility, which lets a foreign central bank swap some of its Treasuries for dollars and buy them back later. The American leg of the intervention was small — Treasury Secretary Scott Bessent's leaked notepad suggested $5–10bn — and funded in an unusual way, by selling euros. Analysts were quick to deride the choice of a third currency, and the sums were trivial next to Japan's. But the point was never the money. It was a signal, to Japan and to the market: a weak yen is now an American problem, not a Japanese one.

The trouble with intervention

That signal matters, because the mechanical intervention largely does not. In under a month Japan spent a record ¥15.4trn ($100bn or so) defending the yen, and the currency still finished little better than it started. The reason is that intervention is a confidence game with finite ammunition, played against a structural force that does not care about confidence.

That force is the carry trade. The yen's chronic weakness is a feature of interest rates, not of politics: for years investors could borrow yen cheaply and park the money in higher-yielding dollars, pocketing the gap. The trade had grown enormous — cross-border yen borrowing reached a record ¥360trn, some $2.35trn, by March, the biggest build-up in three decades. Against a current of that size, even a determined official buying programme is a towel held against a flood. The market grasps the point. In a Reuters poll in early August, some 95% of the roughly 60 strategists surveyed said that intervention on its own would not sustainably curb the yen's weakness, and their yen forecasts were among the most bearish since polling began in the early 1990s.

The lever that actually works

What has moved the yen recently is not an official hand but the expectation of one on the Bank of Japan. The yen has surged about 4.5% in a week to a seven-month high near ¥153, because the market now assigns a near-certain probability — around 97% — that the central bank will raise its policy rate on September 18th, to 1.25%, a level not seen in decades. A rate hike makes holding yen more rewarding, and so investors who had been shorting the currency are scrambling out of the trade. The mechanism is the same one that rattled global markets in August 2024, when a sudden Bank of Japan move triggered a violent unwinding of carry trades; this time the process looks less disorderly, because investors were braced for it. But it is the same lesson: the yen moves on rates, not on propaganda.

The implications for an American investor are real even if the yen never appears in their portfolio. First, the dollar. Washington's willingness to intervene at all — an "era of foreign-currency activism" that began with last year's stabilisation of the Argentine peso — is a mild headwind for the greenback, which strategists expect to soften later in the year. Because American portfolios are so dollar-centric, that is a tailwind they rarely count, boosting the value of overseas holdings.

Second, Japan itself. The boom in Japanese equities this year was built on a weak yen: exporters such as Toyota, Hitachi, Sony and Tokyo Electron rode the currency to a market that set records in April and that has outpaced the world even after the yen's bounce. A deliberately stronger yen cuts that support twice over for a dollar-based holder — once in exporter earnings translated back into weaker yen, and once when those profits are converted into dollars. The investor who owns a Japan fund should understand that the tailwind that lifted it is precisely the thing Tokyo and Washington are now, for different reasons, trying to turn off.

The honest reading of the great yen rescue is that it bought time but changed no one's incentives, and nobody involved pretends otherwise. The currency remains cheap by most measures, and the forces that made it so — the interest-rate gap and the carry trade feeding on it — are intact until the Bank of Japan is willing to pay the price of a genuinely stronger yen. That price is a heavier interest bill on a national debt that exceeds 200% of GDP, which is why the bank has hiked so reluctantly. For the retail investor, the lesson is to stop treating the yen's level as an event and to read it as a report on relative interest rates and on a trade that everyone knew could not last forever. The officials can buy time. Only the central bank, and the burden on its balance sheet, can decide how much.