The dev does everything themselves to my knowledge. The models are modified character cards made by others though iirc. Also a lot of the animations look like the default animations Koikatsu has.
I took a look at the game's scenes and looked at the aritst's Pixiv. From what I can tell the only thing the artists does is making the game and texts. The animations are from multiple different animators with their base characters replaced. Admitedly I didn't bother checking all of the gallery, but with the ones I saw, none of them looked like default animations or Kplug derived. The characters are harder to tell where he got them, but I doubt it matter seeing there's a ton of Chainsaw Man character cards floating around.
Still not convinced he commissioned any scenes either. There's quite a few I recognized, but the ones I didn't still seem to be from paid distribution.
