I finished the book!
Overall it was at least good enough to be worth reading, but it felt a bit long and also kind of fluffed up with a ton of unnecessary stuff at times(it kind of felt like the author really didn’t want to skip anything even if it’s just stuff like the characters moving around or resting or whatever that’s not actually all that important). There’s also way too many named characters 
As for the actual mystery, I guess I was right about who the culprit was and that Miki was actually just Magata Shiki, as well as how she was the one that caused the malfunction, and that no one actually entered the room but wrong about the method, mainly the robot being involved and the fact that they’re mother and daughter and not sisters, as well as how the daughter was just born in the room , but to be honest I’m not sure I can accept that the given evidence actually leads to that as the only possibility even if it’s obviously the correct answer since it’s written that way. The only clues I remember being given is really just that Magata Shiki looked younger than she should have and that she had some toys(and the robot) in her room, and I don’t feel like that alone would have to mean she had a daughter, but maybe I overlooked something
I didn’t think about Shindou knowing about stuff, but it would technically have been necessary for my earlier hypothesis to have worked out too(otherwise the helicopter murder wouldn’t have been possible in my version either)
I also found it a bit weird that none of the students seem to have questioned that someone else just randomly rides along with them(I guess she could just have made something that sounded believable up), that absolutely nobody noticed the age difference between Shiki and her daughter(I thought this was weird when I speculated about the sisters having swapped places, but if they’re mother and daughter it doesn’t really seem realistic that they can just trade places with no one noticing), and that nobody noticed the helicopter murder(I don’t feel like it should be that hard to see inside a helicopter if you’re close enough to talk to the pilot)
Aside from that, maybe it’s just me, but the supposed geniuses/smart people didn’t really feel like believable geniuses to me, like how Magata Shiki’s plan relies too much on people just going along with things without thinking everything through or double checking, like the mother/daughter swap, people not noticing the helicopter murder, etc. would probably realistically not all have worked out that perfectly and feels more like pure luck than something particularly “genius-y” and Moe figuring out the super unintuitive daughter thing(which I don’t actually remember us being any evidence for that only works if she has a daughter and not if they’re just sisters) but not some of the more obvious things for some reason. It kind of felt more like the author just magically gave them what they needed and then went “see, they’re super smart!” instead of giving them a believable thought process(but to be fair that’s super common when it comes to “genius” characters in books for some reason).
The rest of it was pretty satisfying though, including most of the solution to the mystery(it’s just a few parts that felt a bit off), how a lot of stuff from earlier on ended up coming back and how the author made decent use of a of stuff from earlier in the book, and aside from the smoking I don’t mind Saikawa that much and Moe seems cool enough. They really need to acquire a sense of self-preservation in case they end up having to solve more murders though(as does absolutely everyone else in this book, really, in particular the one person that actually did go somewhere alone and get killed in an easily predictable fashion)
So I guess I’d give the book a 3/5 or something like that? And I’ll probably read the next book in a while, but probably not immediately just because this one felt so long that I don’t feel ready to start the next book immediately after(unless the next one is a lot shorter, I haven’t checked yet)
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