lastsinz said: Just look at this guy's works over at Pixiv. Very identical style, even with the hair-over-eyes Koishi.
So it is. He must be Rin's room-mate, or assistant, or something. At his Pixiv's gallery there's a pretty dramatic Onikobe Rin-ification starting on what's currently page 6. (say, starting here) to the present. He had a different style and themes before.