It's probably Takuma Noriage. I really don't know why they just let him go and let someone else take the helm, haha.
Oh well, I don't have that much of an issue with it considering he seems to do well once in a while. Though it is odd that they only really use HIM and no one else really...
Ayu could probably hire some kind of talent out of an art university or go with Kouki Tange's design studio 'yellow brain' but instead she keeps using Takuma Noriage ahhhh. I think it's because he has links with the past studio who worked on her older stuff. He is a former employee of RICE MOMOYA and now is part of 'brg'. RICE MOMOYA did the original "A" logos and such.
Basically, all of Ayu's stuff was either done by Takuma Noriage or Shinichi Hara. I think Shinichi Hara was Takuma's senior though...
http://www.shinichi-hara.com/MUSIC_GRAPHIC.html
Shinichi is/was so good~ his absence seems to mean less logos since he is the one who did all of the unique As until around 2009.