Only days ago, the Japanese yen’s descent showed no signs of stopping, having already dropped to a 40-year low. The joint action took on an extra layer of intrigue after a Reuters photograph revealed that a “to-do” list from US Treasury Secretary Scott Bessent during a cabinet meeting indicated he was considering US purchases of US$5 billion to US$10 billion worth of yen. This piece breaks down the possible drivers behind this first yen-buying joint intervention since 1998, what to watch for next and its implications for markets in mainland China and Hong Kong. Why did Japan and the US intervene? Qian Wei, chief analyst of overseas economy and major asset classes at China Securities, said Japan’s intervention was largely about seizing a favourable window, while the US involvement could be aimed at helping limit selling pressure on US Treasuries.