A lot of talk about the unwinding of the Yen carry trade online, basically borrowing JPY at 0% and using it to buy US stocks and Treasuries (at ~5% yield). Worked while JPY was weak but if JPY strengthens then your USD assets are worth less in JPY terms and you owe more (in USD) to the lender. So, assets down, debt up = panic!Why did they plunge so much? Because of 0.25% rise in interest?
Not sure how this would affect Japan's own stock market though.