My first reaction: huh, this is a licensed book in the Kinnikuman franchise, and Kinnikuman isn't even the focal character of the book? I mean, the book is about his disappearance, so the title character barely appears in it!
As mentioned, I am not very familiar with Kinnikuman, but I do know the wrestlers in this series are really, over-the-top super-powered beings, with abilities like flight, teleportation and superhuman strength, so I was instantly interested to see how those kind of powers would be used in a puzzle plot mystery. That said, I was also worried my little knowledge of the series might be an obstacle in terms of being able to enjoy the book, as it is obviously mainly aimed at fans of Kinnikuman, and not general mystery fans. So how does it fare?
Well... let me start right away with the message I can't really recommend this book to just general fans of mystery fiction with no interest in Kinnikuman whatsoever. It drops too much on the reader with minimal context, and while I could still understand it, there was a lot I knew would be more interesting if I knew about these characters and their powers better. It doesn't help that this book mainly has Meat as the protagonist (and not title character Kinnikuman) and it is clearly more a 'for the fans' book. The book has an prologue, and epilogue and four stories for Meat to solve, but each story introduces "new" characters for the reader, which the fan is likely to recognize immediately from the main series, but each story does only the bare minimum to introduce each character, so everything feels very rushed, and characters start to blend together really quickly because some of them have barely five lines before Meat starts explaining whodunit.
In the four chapters, Meat and Kinkotsuman encounter different murders and a theft during their search for Kinnikuman, prompting Meat to solve them quickly because he is in a hurry to find the king. The murders themselves are fairly mundane, but things quickly become crazy when you learn what kind of powers each of the involved wrestlers have, from opening interdimensional wormholes to being able to basically stop time. But this isn't only true of the suspects, but also of the victims, who often have outrageous powers too. So in the end, we do have "normal" mysteries in the sense that the victims and murderers were "equal" in power, only due to the fact everyone has a different range of powers, it can be difficult to figure how each crime was committed. And here we have the main problem of the book that is connected to what I said above: you see, the book has pretty interesting murder set-ups that make good use of the various powers established characters have, using them in original ways to come up with impossible crimes, but because the book is so short and has to rush through every story, each story simply has not time to properly set the stage and tell a story. I have a feeling each story needed to be at least twice as long to properly introduce each suspect, explain their specific powers and play about with pointing fingers at the suspects and thus have a more satisfying tale of detection. As the stories are told now, they may be sufficient for someone who knows who say Buffaloman is and what his personality and power range is, but here it feels a non-fan reader is always two steps behind. So sometimes, things feel unfair, even though they really shouldn't feel as such as they could've been explained and set-up more properly if each story had been longer, instead of presenting new information in the conclusion of each case to the reader.
In the story The Key of 10 Million for example, Meat has to protect a jewel from being stolen by the phantom thief wrestler Lupine, only for the thief to succeed, but solving this case requires some information that probably makes perfect sense for a Kinnikuman fan, but not for me, and it is only explained in the conclusion. Other stories like the title story The Four-Dimensional Murder Art Murder Case and The Revived Victim have good ideas here and there that make good use of the powers of these super-powered wrestlers, but they are explained so poorly they barely feel fair. The final story, The Junikukan Hotel Murder Case, has actually a brilliant, and absolutely horrifying trick, but it really needed at least double the amount of pages to really set-up the whole ordeal and play around with the suspects. The whole book has moments like these, that show the writer does know how to write a mystery story with these characters in the world, but for some reason, they didn't enough necessary meat to the core plot.
So as mentioned in the beginning, Kinnikuman Yojigen Sappou Satsujin Jiken is mostly interesting for existing fans of Kinnikuman, who want to see their familiar characters used in what is essentially an original and adequately written mystery short story collection. For those with basically zero knowledge of the series however, it's written far too hastily, making it feel more unfair than it actually needs to be, as a lot of the problems I have with the book are not with the plots themselves, but more with it being too brief on a lot of relevant topics. The book might be interesting to read if you're fan of shounen battle manga, and want to see how for example a series like Saint Seiya might also work as a mystery story, but otherwise, I think you can safely skip this one.
