The Japanese Yen rebounded against the U$ from June 2007 to March 2009 (left green arrow below) prompted highly levered traders to unwind negative carry by selling stocks (S&P 500 in navy) and paying back Yen-based speculation loans.
More recently, the Yen bottomed against the greenback in mid 2015 (far right green arrow) and the S&P has wobbled, but so far levitated near its highs.
Another scene of interest here is the most recent dshort chart below showing NYSE margin debt (in red) and the S&P 500 (in blue) as at the end of March. From record-ever-in-human-history-highs in April 2015, margin debt has come down 14.3% to date and 2.7% month-over-month.
What happens next? We watch this horror show with interest while peering through fingers over our eyes…pass the popcorn.