I've been watching this Youtube channel where they introduce interesting apartments up for rent in the Tokyo Metropolis area a while now, from apartments that have very weird layouts to rather inventive manners to make incredibly cramped rooms feel somewhat spacious and still have all the utilities you'd expect from an apartment.
An interesting book, with an interesting story behind it. Uketsu is a horror storyteller who is also a Youtube content creator, and originally, this story was one of their 2020 videos, a creepy story about a mysterious floorplan and their attempts at learning what the meaning could be behind the strange kitchen space and the other rooms. This "real estate" mystery was like an urban legend, starting with something very mundane (a house on sale and its floorplan), but then slowly the horror creeps in, leading to a surprise twist revelation. The video was quite popular, leading to Uketsu writing a whole novel based on the video. And now even a film is the making! In the past, I have written short editorials about floorplans in mystery fiction, and the use of (3D) space in mystery fiction (games), which probably is enough of a hint to tell you I quite like floorplans in mystery fiction, so the idea of a mystery tale that revolves around looking at floorplans, finding out what's "off" about them and figuring out what the meaning behind it is, sounded quite alluring.
It is a very short book ultimately, and I feel it's definitely the first chapter, directly based on the original video which is the most fun and surprising. If you just glance at the floorplans, it seems normal enough for a Japanese home, but as you check the rooms and the "dead space", you start to sense there is certainly something not quite normal about this home. Uketsu is introduced as a horror writer, not a mystery writer, and I would say you can definitely feel this from the atmosphere of the story. It's really like one of those urban legends, where something small that doesn't seem quite right turns out to have a surprising and often far-fetched truth, but that's what makes urban legends fun in the first place of course, the irrational horror hiding behind modern, urban elements. But in terms of build-up of the story, it's definitely a proper mystery story, with clues hidden within the floorplans themselves, but also for example what we hear about the previous owners from the real estate agent etc., with theories regarding the seperate curious elements of the house being put on top each other to build a surprising daring tower of connected theories. The theories here of course not "Queen-style" super tight chains of logic that seem to point to the one and only truth, but they are alluring and silly enough that I will gladly "believe" like a good urban legend.
In a way, the weird floorplans in Hen na Ie are very similar to the floorplans you see in the curiously-designed houses in mystery fiction like The Decagon House Murders and Murder in the Crooked House, but at the same time, they are very different because the houses in Hen na Ie should be completely normal buildings, built in normal residential areas and made to house normal nuclear families. And yet, a good look at their plans reveals they are not normal, and that gives off this sense of creepiness, whereas the floorplans in mystery stories like the two mentioned above may look strange due to their shape or because of strange rooms, but there it's almost expected, as you know a murder is going to happen there and that these grotesque houses themselves also play a role. So again, the "horror" element plays a big role in the enjoyment of Hen na Ie, the sense of uneasiness of not expecting such elements in a normal house.
The book is fairly short and written like a non-fiction reportage, consisting mostly out of transcripts of interviews and telephone calls. After the first chapter, we learn about more houses that have these weird characteristics in their layout, and the theory behind the meaning of these layouts grows and grows as the narrator and his friend start comparing the various houses and their floorplans, and guess what the purpose of these houses are. The idea behind the other houses after the first chapter are quite similar in a way, so they aren't as surprising, but part of that is explained due to the connection these places have. But I do feel the ending isn't as satisfying as the set-up of this book. As mentioned, the first chapter really manages to capture the uneasy feeling of an urban legend with the seemingly normal, but actual abnormal floorplan, and even though the narrator and his friend arrive at a theory, you don't really get solid confirmation about whether they are really correct or not, so that feeling of uneasiness stays. But in the last chapter, we do get full confirmation about everything, which is I guess suitable for a normal mystery story, but this was more a horror mystery tale, and in this specific instance, I would have been content with just the idea of people coming up with elaborate theories based on the floorplans (whether they are real or not), as I think the "definite" answer leans a bit too "obviously" into the horror, while I liked it when it was less defined.
But on the whole, I quite enjoyed Hen na Ie as a short read with an original angle. The book is perhaps better as a horror story that uses mystery fiction "grammar" but the focus on the floorplans and also giving the reader a chance to look at the plans first to see if they can figure out what's wrong about the houses and what the meaning of that could be is entertaining, and as someone who loves floorplans in mystery fiction in general, I was pleasantly surprised. It's not a super deep mystery, but perfect as a short inbetweener.