The yen strengthened 3.7% against the dollar in three sessions, falling from 160.39 per dollar on Wednesday to 154.50 by Monday without another confirmed intervention from Tokyo. The move matters for crypto markets because a similar yen surge in August 2024 forced investors to unwind cheap yen-funded trades and sell risk assets, sending Bitcoin and Ethereum down as much as 20%. This time, Bitcoin stayed above $79,000, close to its highest level since May, making the latest currency move a stress test for the trade that damaged crypto in 2024. Japan’s foreign reserves fell $94.6 billion in August to $995 billion, including an $87.8 billion decline in foreign securities that suggested short-dated US Treasuries were sold to finance the defense. Japan Research Institute economist Akira Nishimura said further sales could attract pressure from the US, leaving the Bank of Japan with more responsibility. Markets price around 75 basis points of cumulative rate increases by April 2027, while a quarter-point hike next week would lift rates to 1.25%. BOJ board member Hajime Takata has urged policymakers to act nimbly against rising inflation. The next key question is whether the yen’s advance accelerates, as a more violent move would present a greater test for Bitcoin.