Excellent book.
I like to think of it as a post-modern film noir set in Tokyo, around two sisters named Eri and Mari.

The story follows how their lives connect to each other, an old friend, an abused Chinese prostitute and the keepers of a “love hotel” that found her that way, and the abuser of the Chinese prostitute, all in the course of one night.
The ending was a bit of a letdown, but then aren’t all film noir endings like that?
I came away thinking of it as more of a quick peek into people’s lives when the sun goes down.
And how our natures change in the dark.
In my mind, I expected a clearer ending. It was a quick read.
The resolution we are given is tastefully done and just makes you think for a bit after you close it.