What I picked up were two cards from the "JBR 64: 1962 Showa Memory Sheet Phonograph Record Voice Bromides" set. These are postcard-ish sized (4 3/16" by 5 5/8") cards that have a phonograph record etched into the front of the card. So these are combination baseball cards and 45 RPM records! You can put these on your record player (if you still have one) and listen to the player on the card speak. OK, I'm assuming you can hear the player talk - I haven't actually played them to find out. They might instead have someone narrating the player's life story or include radio highlights of their careers.
There are 27 known cards from this set featuring a lot of the big NPB stars at the time. Sadaharu Oh and Shigeo Nagashima each have three cards and other players featured include Shinichi Eto, Isao Harimoto, Kazuhisa Inao, Masaichi Kaneda and Katsuya Nomura. The two cards I got are the most common cards - one each of the Oh and Nagashima cards. Here's scans of the fronts and backs of each of them:
I am curious what these sound like - I'll have to dig up a turntable and take a listen. Maybe I can record them and run them through Google Translate.