If you look into game files, you will find out that almost all CG are sliced onto ~30 layers to make this effects. It could potentionally overload almost any normal GPU. Also game probably require to run it onto SSD as well.Bad optimization. Bad code. Bad approach. He's overcooking Renpy with too many drawings for whatever effect he uses. Most likely to fix that, he would need to redo entire mechanic. If he ever thinks to make android port, it would kill performance entirely.
P.S. Ayumi face on sprites and some CG looks worse than original.