U.S. Federal Reserve Chair Jerome Powell is "Mr. Yen." He has been for some time, but it has taken a while for the world to catch on.

This is a simplified version of the narrative that emerged after the Japanese currency fell through another big round number — this one being ¥160 per dollar.

You would think Japan has no agency and that something that should have been apparent all year has suddenly come into view: The biggest driver of the yen’s depreciation is the yawning gap in interest rates between Japan and the United States. Even stray yen bulls stake much on the Federal Reserve, reducing borrowing costs later this year.