Sumitani was apparently ready to leave Seibu for Chunichi after the 2015 off-season, but decided against it after someone in the Chunichi organization advised him not to because of General Manager Hiromitsu Ochiai.
Source: ZakZak 9/27/2016
Sumitani will sign a brand ambassador agreement with Mizuno for the 2018 season.
Source: Sports Hochi 11/23/2017
November 25 – The first game Sumitani watched was a Giants game at Tokyo Dome. He cheered for Tatsunori Hara while wearing his number 8 uniform.
Source: Nikkan Sports 11/25/2018