Late on July 30 Beijing time, the US and Japan launched their first joint currency intervention in decades, with markets initially expecting the move to reverse the yen's persistent depreciation. However, judging from subsequent capital flows, this unprecedented market support operation produced an unexpected side effect: the yen's temporary strength actually provided a more favorable entry window for numerous institutional investors, many of whom used the opportunity to increase their carry trade positions.

Despite the intervention briefly pushing the yen higher, it failed to alter the trading logic fostered by Japan's low-interest-rate environment. The significant bond yield differential between Japan and the US remains the core driver of cross-border capital flows, making it difficult to truly resolve the yen's medium-to-long-term depreciation pressure.

Intervention Sparks Temporary Gains, Funds Seize Rally to Deploy Overseas Assets

According to statistics released by Japan's Ministry of Finance, Japanese investors recorded net purchases exceeding 5 trillion yen in overseas stocks and long-term bonds during the two weeks ending August 15, a sharp reversal from the net selling position of over 300 billion yen in the preceding two weeks. Market observers note that this wave of cross-border buying occurred after last month's US-Japan joint intervention boosted the yen, with investors seizing the window of yen strength to allocate overseas assets at more favorable exchange rates.

Jesper Koll, executive director at Monex Group, stated that the currency intervention effectively accelerated the carry trade for fundamental long-term investors. He added that as long as Japan's domestic funding costs remain below returns on overseas assets, carry trades will reclaim their dominant position in the market. Although the official intervention successfully triggered a rapid yen rebound, with the exchange rate rising from around 164 yen per dollar before the intervention to approximately 155, the rally proved short-lived as the yen quickly gave back most of its gains, falling back to around 159. This has led to a market consensus that unless the Bank of Japan implements substantial rate hikes to narrow the spread with the US, the yen will remain under pressure, with the 10-year US-Japan government bond yield differential holding at around 1.8 percentage points as of Thursday. The yen's impulsive surge did not trigger large-scale unwinding of carry trades; instead, it became an opportunity for institutions to rebuild positions.

Institutional Behavior Confirms Trading Logic, Intervention Treats Symptoms Not Causes

This market phenomenon is particularly pronounced among Japanese institutions. Masahiko Loo, fixed income strategist at State Street Investment Management, noted that long-term allocation institutions such as pension funds and asset management firms continue to sell yen-denominated assets. Francis Tan, Asia chief strategist at Indosuez Wealth Management, said the intervention only addressed superficial issues without tackling the core problem. He further explained that the so-called core problem refers to structural realities such as Japan's cheap funding costs and the massive interest rate gap with major economies.

Jesper Koll said Japanese individual and institutional investors are fully exploiting the yen's strength to build substantial positions in non-yen assets, with a focus on higher-yielding US short-term Treasury bills and government bonds. Masahiko Loo noted that compared with the pre-intervention period, the degree of one-way market betting has declined, but as long as the US-Japan yield differential remains elevated, the appeal of using yen funding for cross-border transactions will not disappear. Ashwin Binwani, founder of Alpha Binwani Capital, said institutions continue to maintain carry trade positions across a basket of G10 currencies, with the Australian dollar being a major target. Many traders closed out short positions during the intervention-driven rally, only to re-establish bearish yen positions once the effect faded. He said every yen rebound triggered by intervention becomes a favorable entry point for shorting the yen, with the underlying driver remaining Japan's low interest rate levels.

Speculative Positions Retreat, But Long-Term Exchange Rate Dilemma Remains Unresolved

Data from the US Commodity Futures Trading Commission shows that leveraged funds' net short yen positions have contracted significantly, falling from nearly 138,000 contracts at the end of June to 59,526 contracts by August 11, reflecting that the authorities' clear intervention intentions have created a certain deterrent effect on aggressive speculative capital. However, the contraction in speculative positions does not signal an overall retreat of carry trades; rather, the allocation behavior of long-term institutions such as pension funds and asset managers will be the key factor determining the yen's medium-term trajectory.

Conclusion

In summary, the US-Japan joint intervention achieved short-term exchange rate disruption but cannot alter the interest-rate-differential-dominated capital flow pattern. The yen rebound engineered by the intervention has instead become an opportunity for institutions to increase carry trade exposure. To truly change the yen's weak posture, the Bank of Japan still needs to make substantive adjustments to monetary policy; relying solely on foreign exchange market intervention can only briefly change market rhythm without reversing the underlying structural contradictions.

USD/JPY daily chart Source: Easy Forex

As of 13:44 Beijing time on August 21, USD/JPY was trading at 158.91/92