Well this is just a RUMOR..
I heard it from my friend. He's ayu fans too.
He said that the background of ayu's family isn't like what we read in internet. As we know that ayu's father had left the family when she was three and little ayu lived with her mother and grandmother.
However, my friend said that actually ayu was adopted by Yakuza
after his father had left them... Ayu was bound by a contract to be a singer with Yakuza's family. This fact (he considered it as a fact) was hidden from public, because it is about Yakuza. So only a few people know about this.
He also said that there was a video in Japan which is canceled to be distributed because it tells about ayu's family (the yakuza one).
Any ideas ?