The first walk off grand slam in a Nippon Series was hit by Toru Sugiura of the Swallows against the Lions in Game One of the 1992 Series. Sugiura was pinch hitting in the bottom of the twelfth inning. Here's video of the entire inning - Sugiura's at bat starts around the 11 minute mark:
The first sayanora home run in a Series game in Fighters franshise history was hit by Koichi Iwashita of the then-Toei Flyers in Game Five of the 1962 Series off of future Hall Of Famer Masaaki Koyama of the Hanshin Tigers. Iwashita's home run was a two run homer that was hit in the eleventh inning. I found this video on YouTube that appears to be a biography of Hall Of Fame manager Shigeru Mizuhara who managed the 1962 Flyers. Kinoshita's home run is around the nine minute mark:
There are a lot of baseball cards available for Sugiura. He had a 22 year career with Yakult that ended in 1993 so he appears on a number of Calbee and Takara issues as well as the first three years of BBM's sets. He has not appeared in many of BBM's OB sets however - I think he's only shown up in four of them (2002 All Time Heroes, 2009 Back To The 80's, 2009 Yakult 40th Anniversary and 2013 Greatest Games - 10-16-1985). His 1992 BBM Nippon Series set card shows his bat flip after hitting the grand slam:
|1992 BBM Nippon Series #S43|
|1967 Kabaya-Leaf #406|
UPDATE - forgot I wanted to credit Deanna and tensaibaka of NPB Reddit with the information on Sugiura and Iwashita and my friend Hiro for sharing the video of Sugiura on his Facebook page.