For some reason, I always mix up Nishizawa Yasuhiko and Yonezawa Honobu in my head. They write completely different type of stories, but I always have to make sure I'm thinking of the right name/right titles when it comes to these two.
The last few years, Hisatarou has been spending New Year at his grandfather Reijirou's place. One shouldn't imagine a nice family gathering though. Half a lifetime ago, Fuchigami Reijirou was a horrible father, always drinking and gambling. When his wife died, his oldest daughter Kamiji and youngest daughter Haruna both left, leaving Reijirou and the middle daughter Kotono all alone. Kamiji and Haruna both cut ties with their old family, got married and took the name of their husbands. Reijirou at some time planned to commit suicide together with Kotono, but heaven had different plans for him: he won a fortune at the horse races, and with the money, Reijirou and Kotono started their own restaurant, which would eventually grow into the nationwide Edge Up restaurant chain. Both Kamiji and Haruna tried to rekindle their old family bonds after this, but Reijirou never forgave his daughters for leaving him and Kotono. However, recently the elderly Reijirou has softened up, as he has started to think about his inheritance. Obviously, loyal Kotono will inherit all of Reijirou's belongings, but she has no children of her own. Reijirou therefore wants Kotono to legally adopt someone to become the Fuchigami heir. The obvious candidates are Reijirou's grandchildren: Hisatarou and his two older brothers (the three sons of Kamiji) or the daughters of Haruna. But there are also other candidates, like the secretaries of both Kotono and Reijirou. The New Year gatherings are therefore used to get on Reijirou's good side by Kamiji and Haruna, who both hope their own child will be chosen.
For as long as he can remember, Hisatarou has had the curious ability to get stuck in time-loops. Once every few weeks, he'd get stuck like in Groundhog Day: he'd live through a day and at the strike of midnight, he'd find himself back at the start of the same day. Nobody else is aware of this time-loop and in general, everyone acts the same in every loop unless Hisatarou does something significantly different which alters the stream of time. It's thanks to this ability he passed the entrance exams for school, because he happened to get stuck in a loop on exam day and thus became aware of the questions in advance. Hisatarou can not actively control this ability however and the time-loop happens completely random. Soon after New Year, Hisatarou finds himself stuck in another of these time-loops, but to his great shock his grandfather Reijirou is murdered during the second loop of the day, even though nothing happened the first time. Hisatarou realizes he must've done something wrong in the second loop which ultimately led to his grandfather's death, so he tries to prevent Reijirou's murder in subsequent loops, but each time, unforeseen happenings eventually result in his grandfather's death. From experience Hisatarou knows he will relive the same day for a total of nine times and that the ninth loop is final, so he has to find a way to prevent his grandfather's murder before he gets unstuck again and advances to "tomorrow" in Nishizawa Yasuhiko's Nanakai Shinda Otoko ("The Man Who Died Seven Times", 1995).
You don't have to read much of Nishizawa's work to realize that the incorporation of science-fiction and fantasy elements is the defining feature of his writing style. I never reviewed Nendou Misshitsu ("Psychokinetic Locked Room!") properly here even though I read it for a book club once, but that was a really unique short story collection where people had psychokinetic powers, but that still allowed for fun and fair locked room murder mysteries, despite the fact people could literally lock a door from the other side with mumbojumbo powers. Nanakai Shinda Otoko is perhaps Nishizawa's best-known science-fiction mystery novel. I've had the book for years by the way, but I didn't really get into it for err, reasons.
Anyway, the time loop is a popular trope in mystery-themed videogames, but not so much in "traditional" novels. Obviously, the Groundhog Day-type of time loop is very closely related to videogames in general. Say, you play a game of Super Mario Brothers and you fall in a pit somewhere. If you restart the level, the player (=you) are experiencing a loop: you went 'back in time' to redo the level (restarting a part), while retaining your knowledge of the previous loops. Eventually, you learn to get past this part, partially due to the knowledge gained through the loops. The player is thus always time-looping. There are also mystery games that make use of this meta-looping, that build on the idea that a player can die and redo a part. In Rei-Jin-G-Lu-P for example you must die several times first to gain the knowledge that allows you to get past that part. The Kamaitachi no Yoru games aren't formally about time-loops, but it does give you hints in the bad endings that allow you to make the right choices afterwards.
It's pretty interesting to see this trope used in a 1995 mystery novel though, and I have to say Nishizawa did a really great job. While the story is essentially about a young man reliving the day his grandfather dies over and over again, the overall tone of the novel is fairly lighthearted and comedic. The first time Reijirou is murdered, it's very easy to guess who killed the man, so Hisatarou's plan is to keep them busy during the second loop so the murder can't be committed. This action however puts the other people in the house "off-course" too, and the Butterfly Effect eventually still results in Reijirou's murder. It's funny to see how Hisatarou tries to gently pull the strings of everybody to coax them into doing what he wants them to do each loop, and how these actions still manage to result in his grandfather's death. The story has a bit of a slapstick element to it, but at the core, it's still a detective. At the start of each loop, Hisatarou reflects back on the previous loop to see what went wrong and the reader can think along too and identify the little thing Hisatarou overlooked.
While the murders each loop won't feel very weighty on their own, there's definitely build-up to the climax. Hisatarou has to make sure that on the ninth and final loop, his grandfather does not die and to do so, he has to remember all that has happened the previous loops and use that to his own advantage. The clues are hidden across the various loops and it's nice to see how everything comes together at the end, with scenes in one loop turning out to be of importance to reinterpret events in other loops. But even after everything seems to have settled down, there's more for Hisatarou to do, as over the course of the nine loops, he also encountered a few events that still puzzle him and this is where the novel really goes all-out in utilizing the loop structure to its fullest, bringing all the scattered hints across time together to reveal a surprising truth. What I like about it that ultimately, this final mystery is only visible to Hisatarou and the reader: the mystery only arises because we were all able to experience the same day several times from various angles, while for the other characters, there was never a time loop and each day only happened once. It's a very interesting way to create a mystery plot, and it was handled well in this novel.
And I think Nanakai Shinda Otoko's merits also lie in its accessibility. "Science-fiction mystery" might sound hard to grasp at first, but this novel is written in a way that makes the time loop plot device surprisingly easy to understand, even if you're not familiar with the trope. To then write a mystery story that does make use of the time loop in a clever, fairly-clewed manner, but without getting overly complex or too science-fiction-y, is probably easier said than done, but Nishizawa succeeded with this novel. A very amusing novel that can be surprisingly cleverly plotted despite its accessibility.
Original Japanese title(s): 西澤保彦『七回死んだ男』