Spiral ~ Suiri no Kizuna or Spiral ~ The Bonds of Reasoning was a mystery(-themed) manga created by writer Shirodaira Kyou and artist Mizuno Eita which ran from 1999 until 2005, and which also saw an anime adaptation in 2002. The series was about Ayumu, who lives with his sister-in-law Madoka after his brother Kiyotaka disappeared. Kiyotaka was a true prodigy, talented at everything he did and his brilliant mind was put to good use as he was a police detective, but two years ago, Kiyotaka disappeared after a final phone call with Ayumu where he mentioned the phrase "Blade Children". At the start of the series, Ayumu gets involved in a murder case that occurs at his school, but with the help of the school newspaper club president Hiyono, he manages to prove his innocence, only to learn that this murder involved the Blade Children and that he himself, as the younger brother of Kiyotaka, has become involved with this affair too. This is the start of an adventure where Ayumu and Hiyono start digging in the mystery of the Blade Children, which however is not without danger for themselves and more often than not, Ayumu finds himself forced into deadly games of life and death to get to the truth. While the first volume or so might make Spiral ~ The Bonds of Reasoning look like Detective Conan or Kindaichi Shounen no Jikenbo with 'a case of the week', it soon becomes a very different series, focusing more on deadly strategic games where Ayumu has to fight for survival with his mind, and the last third/ending of the series is probably not at all like you'd expect based on the first chapter,
Author Shirodaira Kyou also wrote four novels set in the world of Spiral ~ The Bonds of Reasoning (with illustrations by artist Mizuno), and in general, they seem to have been received pretty well, so I always wanted to read them, and recently, I managed to get hold of them. The first one I read is not the first on the series though: I started with the second one, because it was often referred to as the best in the series and I even sometimes saw references to the book outside of a Spiral ~ The Bonds of Reasoning context, so just on its merits as a mystery novel! Spiral ~ Suiri no Kizuna 2: Koutetsu Banchou no Misshitsu ("Spiral ~ The Bonds of Reasoning 2: The Locked Room of the Steel Gang Boss") was first released in 2002 and as I am typing this, I was paging through my own copy, which was apparently from the 14th printing run in 2004, so I guess this book sold reasonably well to have at least so many print runs! The book has no direct ties to the main series, so you could get pretty easily into it without any prior knowledge of the series, as it is clearly set very early in the series' timeline, when most of the Super Dramatic Events haven't happened yet. You could easily read it after just reading the first volume of the manga or watching the first few episodes. The book opens with a nightly visit to the convenience store by Ayumu, when he witnesses a girl dancing on the street. The girl feels offended by Ayumu's staring eyes, while Ayumu is offended by her dancing in the street for everybody to see, and after a bit of bickering, the girl orders Ayumu she never wants to see him again, but also gives him a metal badge with the kanji for "steel" etched into it, telling him to keep it safe. The following day, when Ayumu is loofing around in the newspaper club's office, Hiyono immediately recognizes the badge as the one once owned by the "Steel Banchou" or "Steel Gang Boss" about five decades ago. She tells about the Golden Age of School Gangs, when juvenile delinquents at schools across the country formed gangs who would gather under charismatic "banchou" (gang bosses) like the Magic Gang Boss or Pistol Gang Boss, and how ultimately the dramatic suicide of the Steel Gang Boss prevented a nation-wide gang war. Ayumu buys nothing of Hiyono's story, but then the mysterious girl, who happens to be a student at their school too, appears in the club office. At first it appears she wanted to hire Hiyono to locate "the boy she gave a badge to", but finally noticing Ayumu in the room and being too proud to admit she wants the badge back, she changes her request to Hiyono (and Ayumu): she wants them to prove that contrary to what is believed, the Steel Boss didn't commit suicide, but was in fact murdered inside a locked room and by doing so, destroy the nearly fifty-year old legend of the Steel Boss who gave his life to prevent a war.Okay, I have to admit this book wasn't at all what I had expected of it. For on the whole, this tale isn't really connected to the main Spiral ~ The Bonds of Reasoning series and at times even feels out of place. The only real connections are Ayumu and Hiyono, but the "world-building" presented in this story sounds nothing at all like the rest of the series, which is really odd. It feels more like a story author Shirodaira wanted to write, and he happened to use Spiral ~ The Bonds of Reasoning to tell this story because it would have an established audience of readers already. On the other hand, I can definitely understand why so many readers like this particular novel, and how it is an important novel when seen in a wider context, to be exact, in relation to Shirodaira's later work.
So the book doesn't really feel like a Spiral story, and that's also because almost half of the book consists of excerpts from an in-universe book, being the definitive work on the Golden Age of School Gangs and their wars. This book details how in post-war Japan, juvenile delinquent students started forming gangs at school under the leadership of banchou, who would get into fights with the leaders of other schools. What follows is an absolutely bonkers story about school gang bosses plotting to become the number one boss across the whole of Japan, putting other schools under their control, and in-party power struggles eventually leading to the rise of the Magic Gang Boss and the Pistol Gang Boss, two charismatic leaders who basically each controlled half of the schools in Japan. But when a new leader arrived in the form of the Steel Boss, the balance of powers was disturbed, and things were heading to a nation-wide school war between the three factions, until on the day of the war of the fates, the Steel Boss was found dead inside the little shed he was living in on the riverside. He had taken poison, and the cottage was locked from the inside. A few days later, letters were delivered to the Magic Gang Boss and the Pistol Gang Boss signed by the Steel Boss, where he stated his wishes to stop unnecessary bloodshed and his death should be enough to make everyone realize this, and this became the legend of the Steel Boss. Author Shirodaira obviously has immense fun writing this completely ridiculous story of high school students fighting each other like Warring State period generals, with 'wars' being fought along the riverside and 'clever' strategies and tricks employed by the warring factions, It doesn't feel like it fits Spiral ~ The Bonds of Reasoning, but the world of those stereotypical Japanese school gang delinquents fighting nation-wide wars is just really funny, and while this "history lesson" is really really long, it does set-up the mystery and all the necessary clues to solve the death of the Steel Boss. For the facts say the Steel Gang Boss died drinking poison in a small river-side shed, of which the door was barred from the inside and the window wouldn't open due to a crooked frame. That coupled with the suicide letters sent to the Magic Gang Boss and the Pistol Gang Boss seems to indicate suicide, so can Ayumu prove this was actually not a suicide, but a locked room murder, and can he prove who did this and why?
And this is the point where this book becomes important in the greater context, for we soon learn their client isn't exactly looking for the truth, but she simply wants to destroy the legend of the Steel Gang Boss. And so Ayumu comes up with three different explanations based on the known facts for the death of the Steel Gang Boss that indeed put the Steel Boss' death in a completely different light, changing his death from a honorable suicide to prevent a war, to a one-direction murder. So in a way, Spiral ~ Suiri no Kizuna 2: Koutetsu Banchou no Misshitsu is a kind of direct precursor to Shirodaira's later series Kyokou Suiri (known in English as both Invented Inference and In/Spectre). In Invented Inference, the truth usually often involves something supernatural, and the series detective has to come up with a believable human explanation for the events, so one without the supernatural stuff even though that is the truth. So that series revolves around coming up with believable inferences based on the known facts, but they don't need to be true. Invented Inference is about interpretation and multiple solutions and those are exactly the themes of Spiral ~ Suiri no Kizuna 2: Koutetsu Banchou no Misshitsu: we are told what is likely a factual build-up to the death of the Steel Boss nearly fifty years ago, but Ayumu then comes up with alternate interpretations of the facts that lead to believable theories about the murder of the Steel Boss. And that is quite fun! The basic puzzle pieces are all the same, but by shuffling them and turning some pieces around, you are able to come up with a very different picture. Each of Ayumu's theories seem plausible enough, but make use of clever interpretation of the facts presented in the excerpts from the history on the Golden Age of Gang Bosses, allowing him to "open the locked room" and change the Steel Boss' suicide into a murder and make the Steel Boss a simple "victim" rather than someone who sacrificed himself. The book isn't really long, so the three "solutions" are all fairly simple, but they are supported well by the clues both in terms of "mechanics to create the locked room situation" as well as in motive, and they can be quite surprising. I believe a lot of readers praised this book because it was their first encounter with a mystery novel built around multiple solutions/interpretations, and given that Shirodaira later came up with Invented Inference, I think he himself liked the idea a lot too. The book is more interesting read as a book about motives though than as an actual locked room mystery, but I certainly enjoyed it.
Spiral ~ Suiri no Kizuna 2: Koutetsu Banchou no Misshitsu also contains a short story which is technically a prequel, starrring Ayumu's brother Kiyotaka back when he was in the police force. Apparently, there was a whole series of these short stories published online back when the manga was still being serialized. The four novels would all include these stories with Kiyotaka as extras. This particular story is a pure whodunnit which is split up in two parts, the problem and the solution, so I assume originally, they published the first part online and the solution would be published a bit later, allowing readers some time to guess who the murderer was. As a whodunnit it's pretty simple, and a bit weird because it involves a man creating a robotic hand for himself to commit a murder but stuff happens of course, but it's fun enough considering this was just a short story published on the official site.
Anyway, Spiral ~ Suiri no Kizuna 2: Koutetsu Banchou no Misshitsu is not at all what I had expected. I have read spin-off novels for detective manga series before, like those of Detective Conan and Kindaichi Shounen no Jikenbo, but those novels were written to be like the stories in the manga. Spiral ~ Suiri no Kizuna 2 was clearly not written with such intentions. It is only marginally connected to the Spiral series. but as a mystery story, it's pretty fun, focusing on the concepts of multiple solutions. The story itself, about the student gang wars, is really ridiculous, but you can sense Shirodaira had a lot of fun coming up with that backstory and especially knowing he later went on to write Invented Inference, I think Spiral ~ Suiri no Kizuna 2 is a pretty rewarding mystery.