The yen popped on Thursday, then gave most of it back.
The pattern is the same one currency markets have seen for two weeks. Traders push the yen weaker, then buy it again on fears Japan's Finance Ministry is about to step in.
This time, Japan has already proved it will.
Japan's first intervention came on April 30, after the yen weakened past the 160-per-dollar mark. A second round followed days later, bringing the total cost to the Ministry of Finance to an estimated 10 trillion yen.
The yen briefly traded as strong as the low-155 range during last week's Golden Week holiday, touching about 155.04 per dollar.
That should have ended the test, but it didn't. The yen drifted back toward 157.5 against the dollar earlier this week as the dollar rallied on doubts about the US-Iran ceasefire.
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The simple answer is interest rates. The Bank of Japan's policy rate sits at 0.75%, while the US Federal Reserve has its rate between 3.50% and 3.75%.
That gap of close to three full percentage points pulls money out of Japan and into the US dollar. Until the gap closes, intervention can buy time but not fix the problem.
Japanese Finance Minister Satsuki Katayama recently met with US Treasury Secretary Scott Bessent, and both said they are working together on currency policy. That is Japan's way of saying it has Washington's blessing to spend more.
A defense line that started at 160 yen per dollar has quietly moved up, and traders now see the 157 area as Japan's unofficial floor. Every tick toward that level brings the next intervention bet back into play.
The catch: each test costs Japan billions in reserves, and each one only buys a little more credibility before the market pushes again.
The 157-per-dollar level is the line analysts are focused on, and below it the market expects the Ministry of Finance to act again.
The BOJ's next rate move matters more in the long run, since faster rate hikes from Japan would do more to support the yen than any short-term intervention can.
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