The software is called "Koikatsu" (Or "Koikatsu Party" in the West), and there's an expansion called "Koikatsu Sunshine". All of which can be found on their website or on Steam.
It's developed by the awesome "Illusion Soft", who allow amateur indie devs like myself to use their assets royalty-free! Which is just incredible of them, honestly.
They also made AIS, Honey Select 1 & 2 and various other games, all of which follow the "if you're in indie dev feel free to use our assets!" motto, so if you're interested then check them out!
Oh, and shameless plug: if you own Koikatsu/Party/Sunshine, you can pledge on my Patreon or Subscribestar to gain access to all the CK character cards, so you can put them in the game and play, pose, or do whatever you like with them! :)