A sudden earthquake forces 6 people in a fast food restaurant to take refuge in what seems like a shelter when the restaurant's collapse is nearing. This place however turns out to be a personality switching facility and when they wake up they are situated in an isolated locked up space, with their personalities in swapped bodies, which begin to get murdered soon. Whose personality has murderous intents and what is the motive...?
The motive is indeed almost the most important factor over the whole deduction process since the howdunit rather steps back when this personality switches occur continuously and therefore the culprit also switches around constantly. The whodunit becomes pretty tricky under this circumstances and the best way to deduce the personality with the actual intent to kill, is to get to the whydunit.
As authors like Maya Yutaka convinced me, the whodunit and whydunit can be just as interesting as a complicated howdunit, as long as the culprit's at least a bit unexpected and by all means the tricks must be surprising and brilliantly executed. This novel did not go for eccentric narrative tricks, instead it chose the logical way, which is totally fine since I like this classical approach just as well. In this classical whodunit case however, there must be a distinct motive to be guessed by the reader that convinces him when he comes up with it, so that he can underline this theory concerning the culprit through this idea. And I think that was my main problem concerning the mystery part in this book: I could not come up with a satisfying motive for my theory and the one that was eventually true in the end was not that convincing either. Compared to the other possibilities, certainly. But not convincing enough for me to not discard that theory, which I eventually did since I did not think it was that credible to happen anyway.
Don't get me wrong, this is by no means a bad mystery. Nishizawa Yasuhiko did a great job at showing how orthodox mystery can work within a SF context and setting. However, for me there are 2 ways to please me with a totally logical solution: Either it has to be solvable with an exact method and you have to be satisfied with deducing correctly at the end, or the outcome has to be surprising in a way where you did not expect it but are convinced nonetheless by the reference to previous hints and clues.
The latter are the key factor to how I felt about this, I guess. Nishizawa explains the whole system very thoroughly. I don't think you can misunderstand anything and he also includes a lot of hints. But exactly because it's so clear, there are many almost equally credible possibilities, which hinders in being confident about one of those and even if this exact one turns out to be true in the end, it's somehow too indistinct to swallow.
Nevertheless as soon as the closed circle murders section sets in and considering everything I said above, I can definitely say I enjoyed the mystery part, especially the reasoning by the remaining characters near and during the finale. This sections set in very late, though. The entire first half of the whole book deals with explanation of the system, introduction of the characters and thoughts on personality, identity, human relationships and so on on a philosophical and psychological level. The latter was most interesting for me and continues later on in the book and it can also be found within the main characters' development (which was also fairly well done) and the introduction was of course necessary, but the explanation of several aspects concerning the personality switching device and the whole process the characters are undergoing got a bit tedious for me later on since some things were repeated too often. I understand Nishizawa wanted to make sure any reader will be able to grasp everything so that his mystery turns out to be fair, but I think he really expected the readers to be dumb.
The first half could have been considerably more compact or he could at least have tried to touch more on the philosophical and psychological topics, since among the quick succession murders and the reasoning emerging from there on those were the aspects that are already making this book recommendable. Be aware though that due to the nature of the setting and the focus that is applied you will experience 50% Mystery and 50% Sci-Fi, not 100% from both or a mystery novel with some SF-aspects included as it might seem at first when you read about it somewhere. But as long as you keep that in mind and 'endure' the rather long introduction, this will make for a pretty enjoyable read.