Yep, it is erotica. Other than the sex scenes this wasn't a very good book. Some of the sex scenes were okay but they were definitely told by a man and from a man's POV. That is fine...I guess...
But then there is Yuki. All you really know about Yuki is that she is a school girl. Age is not mentioned, but she calls the couple mommy and daddy. That holds a definite creep factor for me. And Yuki is abused in the book and thanks her abusers for the abuse! At one point she is viciously bitten on her face, another time she is forced to walk home with semen hanging off of her face...there are more examples.
I think this book is more geared towards men anyhow. There are scenes where the male character is punching his wife in the ribs (during sex) and the entire book is written with the main male character (Chris) as being the alpha male of both of the women he has at his beck and call.
Some of this was just disturbing. When the married couple heads back home, Yuki is young enough still to return to her parents...how young was this girl in the book? It's possible that the author doesn't specify this to allow the reader to imagine she is whatever age they want her to be...But, yuck.
Anyhow, three stars for the story. I almost two starred this but gave the author an extra star for the imaginative sexual content.