Koikatsu character card. All the character models were designed using Koikatsu, which means there's a character card that has all the detailing of the model that was used to make them look the way they do, and if someone has the card, they can use it for their own purposes (either for custom scenarios in Koikatsu, or to make their own game using the assets).
In the very early days of the game, the cards were available as a Patron perk, but they were removed pretty quickly because people were using them in their own games, and the developer didn't take kindly to that.