Thank you for showing us this formation. If it is a S-H-S then the potential shall be at its end because of as you show it in your chart the black trend line has about the same distance to the neckline as the hight of the head. So in my opinion we should expect an upward retracement now to close the downward gap. In its result we will see whether is is already a change of the trend of the Nikkei.
I have noticed there are many expectations about a long-term trend reversal to the downside in Nikkei. One of the reasons is that the index has hit the downward trend line to be observed on a monthly time frame.