The yen briefly rallied 0.4% to 156.5 per US dollar on September 29 as diplomats issued a fresh warning over the speed of its decline. Top currency diplomat Mimura stated that both Japanese and US officials are increasingly concerned that the currency will weaken further and may take action to support it. He urged market participants to heed a "very clear" warning and dismissed claims that funding constraints would limit Tokyo's ability to conduct buying operations.

The currency later faded to 157.4 per dollar, though it remains up approximately 1.5% for the month. Tokyo spent a record $96 billion on market operations during July and August, following the first joint FX intervention with the US in 15 years in July. In the week ending September 22, leveraged traders cut bullish yen positions by nearly 80% to $355 million, and 1-year Dollar-Yen risk reversals fell to their lowest level since late January.