Long, Intermediate & short term; Nikkei is in a major Uptrend started from June 2016 & confirmed from November 2016, the major uptrend will end if the index value breaks 19239.50 (September 2017 Bottom) downwards.
Next station will be at "June 1996 peak" which recorded as 22531 & it will act as a resistance.
Weakness indication appears on all time frames by several technical indicators such as MACD & Histogram both show negative divergence.
Another technical indicator which is the Money Flow Index "MFI" (momentum + volume) also shows negative divergence & I could draw some helping lines on it (refer to the chart here/above).
I prefer to wait & see How will this Month (Oct.) end (Close) , all probabilities may really occur.
may start selling (short) from 22531 ?
may start selling (short) from testing the last declining help line (as if it is a resistance) applied on the MFI ?
may start selling (short) if this month's candle close below any trend line applied on the monthly chart.
I wouldn't be surprise if the index value continue rising above 22531 & that's cause it still didn't reach the extreme overbought / exhaustion / melting up phase yet, there is some space for more upward move but not for very long.