This is the second Miyabe novel I read, the first being Shadow Family. First thing I should note that if you've read All She Was Worth/Kash and Shadow Family first, please read Devil's Whisper with an open mind and no expectations. One thing I realized about Miyabe's novels, is that although in US she is categorized as a Mystery author, in reality she's a "jack of all trades." She writes every genre, and often mixing them. For example, Crossfire is more like an action/thriller/paranormal type where as Shadow Family is purely mystery to the core (and a short study on family and nature of humans). In the case of Devil's Whisper, it is definitely a mix, with a prominence in mystery, and some leaning toward other genre. Therefore, PLEASE read this with an open mind.
That said, unlike Shadow Family, Devil's Whisper does have a main character who gets developed as the story goes on. Mamoru is a 16 year old boy who has a slightly "dirty" past regarding his parents and where he came from. Despite all the pain he went through as a child, he grew up as a fine boy and has a strong character. When a girl got killed by his Taxi-driver Uncle (whom he lives with along with his Aunt and cousin after his mother's death), he decided to help his Uncle by researching into the girl who died. What he found out was more than just what happened with the girl who died, or her past, but also what happened in his own past.
Weirdly enough, despite Mamoru being a well fleshed out character, I find myself unable to truly connect with him. Even now after reading the novel and finding out the truth, I find myself unable to accept or sometimes even understand the choices he made. Maybe it's something that's lost in translation, but Mamoru also came across as someone without emotion, except a bit of anger, and a lot of fear at one point in the novel. What I received from him was slightly more on the "depressing" side, which perhaps is what made it very difficult for me to connect with him. So oddly enough, rather than connecting with him as a "friend" or "another side of me" (which is what books usually try to do, in order to pull in the viewer), I find myself feeling like his "older sister," wanting to reprimand him on some of his decisions, and feeling perplexed as to the choices he made. But again, maybe this is something that was just lost in translation.
The resolution is also a bit on the unconventional side of mystery. I don't want to give anything away, but I do suggest the reader to view with open mind and give the book a chance, and make your decisions at the end after everything's said and done. At the very least, the first 3/4th of the book was extremely enjoyable, with the last 1/4th of the book slightly on the unconventional but still interesting side.