Japan's currency has gained by almost a quarter against the US dollar this year and a third against the euro, making life even harder for the country's exporters, such as Sony and Toyota. Yet Tokyo is unlikely to halt the rise, out of concern over its relations with the United States, its key ally.

Japan's concern to maintain relations with the United States, its closest ally, on an even keel means Tokyo will seek to allow its currency to continue its steady appreciation, despite the profit erosion this causes in the key exporting sector.