The media learned on November 20 that Motohiro Shima is planning to step down as Chairman of the Japan Professional Baseball Players Association (JPBPA) on December 7, 2017. Shima took over as chairman in November 2012 after Takahiro Arai. Shima became the first chairman from the Pacific League.
According to Nikkan Sports, Ginjiro Sumitani is a strong candidate to take over as the next chairman.
[UPDATE 12/4 @ 2:42pm]
Other candidates include Katsuya Kakunaka and Yuya Hasegawa.
Source: Daily Sports 12/4/2017