It seems that Yamasaki Masato is actually a writer. If you check out his homepage at http://www.yama3.sakura.ne.jp/ you'll see that he works with a lot of artists, writing the stories for their comics. Also he says as much in his profile.
The kanji '作画' means 'artist' and '原作' means 'writer'. There's a circle named after Yamasaki Masato(山咲まさと), the 'dennou yamasaki gumi'(電脳山咲組, 'cyber yamasaki team'), seems to be a group of artist cooperating with yamasaki, including Mr. Izayoi. So don't just tag 'Izayoi_Seishin(十六夜清心)' on every picture from the pixiv id '山咲まさと'. Here the artist of this picture is Shinobu(詩乃譜). Below is the doujinshidb page for this artist. http://doujinshi.mugimugi.org/browse/author/29088/