With my wonderful memory for details having been demonstrated for a number of years now, it probably will not surprise anyone to learn that I am not sure which of Ryuushi's advisors Kouyu is. I believe he is the one who is forever lost (which somehow is fully appropriate to this situation). He's one of several advisors who is in the background for most of the first season and is taking on a greater importance in the second, currently underway. He mostly disapproves of Ryuushi.