I remember coming across the animation of this years ago. Back then I was surprised to find an artist for a big name anime/manga like Mahoromatic making full on hentai. Now it's pretty obvious, someone who draws alot of sexy girls in racey scenes has to have had practice drawing porn.

As I recall the artist for Omamori Himari also did alot of hentai before making that series and Yui Haga with Lotte no Omocha.

I'm sure there were more from back then but my memory is trash.

Come to think of it has Yabuki Kentarou ever done hentai works even under a different pen name? To Love-ru Darkness was so very borderline.