Asako is a popular actress. She was also Rei's girlfriend who dumped him to concentrate on her acting career, which partly triggered his downward spiral to homeless bum. She did not know that Rei would end up homeless. When she finds Rei again, she wants to get back together, but Rei says that he belongs to Sana now, and can't be with Asako until Sana grows up. When Sana realizes (with Akito's help) that Rei is not her "pimp" nor her boyfriend, Asako and Rei reunite. Asako continues to recur until the end of the series.
From: Wikipedia.org