The visuals are done with Koikatsu.
It’s a game with a character creator, but most people use it as a 3d poser.
There are a lot of games made using it out there.
Arc would probably be more positive and encouraging than me.
But I gotta warn you. CK was among the first games made using Koikatsu way back in 2019. Now there’s a ton of games trying to stand out from the rest.