Japan confirmed that it bought yen in coordination with the US Treasury, while Reuters reported that the US funded its part by selling euros. The distinction matters: buying yen with euros starts in EUR/JPY, then spreads across the dollar pairs through cross-rate repricing and the policy signal.
EUR/JPY = EUR/USD × USD/JPY means the dollar pairs must reprice too, but it does not determine which one absorbs more of the move.What happened
USD/JPY touched 163.74 on July 30, near a four-decade yen low, then fell as far as 155.32 within three trading sessions. Japan's Ministry of Finance confirmed that it bought yen on July 31 in coordination with the US Treasury and said it would not hesitate to intervene jointly again.
Two market sources told Reuters that the US bought yen with euros rather than dollars, confirming an earlier Financial Times report. Japan's statement does not identify the currency sold by the US, and neither the Treasury nor the New York Fed publicly confirmed that funding leg. The euro detail is therefore well-sourced reporting, not yet an official transaction disclosure.
Why selling euros changes the first pair that moves
The reported US order sold EUR and bought JPY. Its first mechanical effect was therefore a lower EUR/JPY rate: one euro bought fewer yen as the yen strengthened. The New York Fed explains that it executes Treasury-directed intervention as fiscal agent and that US foreign-exchange reserves are held in euros and yen.
EUR/JPY does not move independently. The three major pairs must satisfy EUR/JPY = EUR/USD × USD/JPY, and banks reprice them almost instantly. EUR/USD can fall, USD/JPY can fall, or both can move. The equation fixes the relationship among the rates, not which market absorbs the order.
If the US does it again
The most reliable directional statement is the narrow one: another euro-funded yen purchase directly pushes EUR/JPY lower while it is executed. A broader yen rally becomes more likely if Japan also sells dollars, the operation is large, or traders expect further intervention. Persistence still depends on the forces that weakened the yen in the first place, including interest-rate differences, positioning, and energy-import costs. This is a map of the transmission, not an exchange-rate forecast.
What the data shows
Between the July 30 and August 3 ECB daily fixes, EUR/JPY fell from 186.99 to 180.73 (-3.35%) and USD/JPY fell from 162.94 to 156.68 (-3.84%). EUR/USD moved the other way, rising from 1.1476 to 1.1535 (+0.51%). The yen strengthened against both currencies, but the euro did not weaken against the dollar over the full window. Japan's activity, the reported US order, position-closing, and expectations of another intervention all sit inside those moves, so the daily observations cannot assign a separate effect to each cause.
The episode also shows the limit of daily FX data. The ECB series recorded USD/JPY at 162.94 on July 30, 160.235 on July 31, and 156.68 on August 3. It contains neither the 163.74 high nor the 155.32 low. Daily reference rates work for accounting and historical analysis; an alert or current-rate display needs an intraday source with timestamps and session context. The live USD/JPY page carries source, market_session, and data_updated_at on every observation.
Selling euros to buy yen tells you which cross receives the order. It does not, by itself, tell you where EUR/USD or USD/JPY will finish.