This has been a pattern for the Nikkei that I have been looking at for the past year or two. You can find it in my blog in at least 3 different places. This pattern is an expanding diagonal triangle in Elliotte Wave lingo; in English it is an expanding wedge. A recent example where this occurred was with Ford when it dived to about $1.
As far as I know no other EW practitioner has had this possibility in mind, so it is pretty unique. Today (the chart is not updated) we are at about 8900. The low does not have to occur on the trend-line as often the low is reached well before that point is reached. It seldom exceeds that point. Even so a meaningful second down leg should be about 5000 points from the 10k level of the B-wave of wave 5. Lets hope I am dead wrong. Below is another chart from about a year ago.