The base set of this year's edition contains 36 cards and features 36 players - I say that because some of the earlier editions of the set had multiple cards for players. Most of the big name retirees from last year are included - Koji Uehara, Shinnosuke Abe, Kazuya Fukuura, Kensuke Tanaka, Toshiaki Imae, Shohei Tateyama and Kazuhiro Hatakeyama. Probably the biggest Japanese player not included was Ichiro but I'm not sure any Japanese player who retired from an MLB team has ever been included in the set (although off hand the only other one I can think of who retired frm an MLB team since BBM started publishing this set is Hideki Matsui and he retired in December of 2012, right when the 2013 edition would have been going to press). The set doesn't included several foreign players who retired last year (Randy Messenger, Brad Eldred and Scott Mathieson) but I think Alex Ramirez is the only foreign player who ever made one of these sets.
Nine of the cards feature photos from the player's retirement ceremony including several who are receiving their do-age from their teammates. All the players are depicted in their most recent NPB uniform, even if that's not particularly representative of their career. For example, both Hayato Terahara and Itaru Hashimoto are shown in the uniforms of their 2019 teams (the Swallows and Eagles respectively) despite them both only spending that season with those teams. Sho Aranami had spent 2019 playing in Mexico and so is shown with the Baystars, his team from 2018. Here's a couple example cards:
This set is pretty much the same from year to year but for some reason I like it. You can see all the cards over at Jambalaya.