Sound and character are also good. The boy is budhist monk and the demon cares about nothing more than sex. I don't notice sound unless it's really bad.
Now for the problem.
While the art is fine, the animation is horrible. Every still frame looks good, but they put minimal effort into animating the scenes. Personally, I can't fully enjoy a hentai without proper animation, so this brought my overall score down to a 6. If you're fine with middle school level animation, then this is a good OVA, but I otherwise suggest you pass. As an example, the animation of a blow job was only one tier above just dragging the image of her head up and down where his dick is supposed to be. In fact, the comment board on Hentai Haven was almost entirely about the bad animation.
