Oh I couldn't play the game yet so I thought that some pictures were not drawn using a game engine.
But that doesn't mean I won't play it.
Oh my bad, I see now! Art styles. I use Krita, it has a pixel brush (and a grid at near-full zoom) and I draw all pictures for H-Scenes to 512px/512px. Anything else will be scaled to multitudes of 16/16, 32/32 or 64/64 depending on its in-world size. (Also 99% of the pictures are only two colors: white and transparent so I can have a consistent BG)
Unity has some things that line the art up well and some post-processing(PP) that give's some effects (If you want to check a before/after of just how much PP contributes: there is a button to turn off screen effects when you get the game).
Hope that helps!