Hi, not peanut, but based on my observations and what others have said, it looks like the game itself is made in Ren'py (a python game engine which is used for visual novels), while the visuals are made in Koikatsu Party (A combination visual novel and anime character creator/poser). I imagine that it was done by moding Koikatsu because the models don't normally look like this in base, but I could be wrong. Hope this helps until the devs answer directly :)