Was going to comment on the dark scenes, but there's already a bit of conversation regarding them.
The idea of "natural" lighting in a VN like this doesn't have to be pure "natural". I completely get the artistic side of it, but making it where it's near pitch black in scenes defeats the entire purpose of the scene. Plus I've never been in a sauna that's dark like that, they're always well lit. But I digress, I enjoy the VN, just wish several scenes had better environment lighting settings (either changing the environment light settings, or adding a emitter plane at the top of the room to give a downward light).
Edit: So I looked at the sauna scene again, and realized there's at minimum 9 light sources (I want to say upwards of 15 actually). In "real life" that place should be extremely well lit. Even if it were just the candles shown in the scene it'd be fully lit.