Tokyo's reserves fell $88bn. We can guess what it sold.
The biggest seller of US government bonds in the August rout was a friendly central bank doing something it had no choice about, and that is precisely the kind of selling no speech from the Federal Reserve can talk down.
Japan's Finance Ministry said on Monday that its holdings of foreign securities fell by $87.8bn in August, the largest monthly drop it has ever recorded. It had already admitted spending ¥15.4tn ($98.6bn) to prop up the yen in the month to August 26, also a record. The two figures are close enough that analysts quoted by Bloomberg conclude Tokyo paid for the rescue by selling US government bonds, most likely ones due to be repaid soon. A ministry official would say only that intervention was "a factor" behind the fall. The mechanics are not complicated. To buy yen you have to sell dollars, and Japan keeps most of its dollars in US government bonds. So the harder Tokyo defends its currency, the more of Washington's debt lands on the market, and this happened in the same weeks that the rate the US government pays to borrow for ten years (the 10-year) reached 4.82%, its highest since 2023, and Treasury Secretary Bessent doubled the department's purchases of its own long-dated bonds to at least $4bn per operation from September 9. None of this was hostile. The United States joined the yen operation on July 31, the first time the two countries acted together on the currency since 1998. It is still one of the largest holders of US government bonds selling into a falling market. What makes it worth watching is that it feeds itself. High American interest rates weaken the yen; Japan sells US bonds to buy yen; the supply of US bonds goes up. Sales of bonds due soon do less damage to long-term borrowing costs than the headline suggests, and we do not know what mix Japan sold. But Japan's own government now pays more than 3% to borrow for ten years, the first time since 1996, which gives Japanese money one less reason to stay in dollars at all. Put that beside the rest of the ledger. Norway's sovereign fund has proposed cutting roughly $80bn from the $215bn of US government bonds it holds, though not before 2027. Chinese commercial banks are buying, paying 3–4% on the dollar deposits that fund the purchases. The Treasury Department starts buying back its own bonds today. The sellers are governments. The buyers are either borrowing to do it or are the issuer itself. That is why this sits in fragility rather than ignition: nothing caught fire, but the natural buyers are leaving.