Let me preface this by saying I think this is an example of a narrative being backfitted to a move.
Anyway ...
"Gotobi" refers to the practice in Japan of making certain payments on specific days of the month.
The term "gotobi" can be translated as "every fifth day." This means that these payments typically happen on days that end in a "5" or "0" (like the 5th, 10th, 15th, 20th, 25th, and 30th of the month).
For many Japanese companies, especially in industries like exporting, "gotobi" days are significant because they are the typical days for settling accounts and making or receiving payments. This can lead to increased activity in banking and financial services on these days.
And indeed, some chatter in the market is attributing the fall in USD/JPY to Gotobi today, with the Tokyo fix showing more exporter than importer interest. Exporters receive offshore currency and have to convert it (perhaps not all) into yen to pay suppliers, employees and what have you.
As an aside, importer bids are chunky down to 148.00 now.
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As some support for my scepticism, the USD is lower across the major's board, its not just a yen move.
