Specifically, it reads like less of an attempt to construct a good story, and more like a thinly-veiled warning to young girls, with Ayu only used as a puppet rather than a proper character. Which has a dark humor to it, considering how she is "used" not only by the men who buy her, but also the author, only to be discarded after she's served her purpose. And if the author himself treats his own main character like this, how am I supposed to see her as anything more?
Thus, all these bad things that happen to Ayu in such a short amount of time don't feel organic, but like the universe has it out for her. Literally every plot point is predictable, and the story loses any tension or interest because you know that anytime something good is given to Ayu, it will be yanked away from her eventually and leave her in deeper despair — which, in turn, makes the story melodramatic instead of somber.
And this is the main problem: the story lacks sympathy for Ayu. Sure, her life is plenty sad, but there is no attempt made to explain how she got to this point. She serves no purpose other than to be The Girl Whom Bad Things Happen To; who, despite feeling dirty, still sacrifices herself for everyone around her to the point of her own demise. She is not a realistic character, but a punching bag, a doll to be pointed at when saying "don't be like this".
That's not even getting into the saccharine moments, like the dog magically knowing where to find everyone, or the homeless man comparing Ayu to an angel (wow, so deep).
While the art was OK, the black text boxes were annoying, in that they only reiterated the obvious. As if the message isn't blatantly clear, the author feels that he must spell it out for the reader, as if they were some small child incapable of figuring it out on their own. Considering the mature themes of the manga, this comes across as belittling.
All in all, this manga was a disappointment. I expected a sad story that didn't pull punches, with a somber tone and depictions of real situations. Instead of that, I got a melodramatic mess that reads like it was plotted in an hour by someone who wanted to scare teenage girls away from prostitution.