Thank you all for the great suggestions! Keep them coming!
They both sound very interesting, I’m putting them on my list. They might not be ideal as a first book though if there’s old-fashioned language involved. There’s some old-fashioned language in Ogawa Mimei’s stories that we’re currently reading in the Beginner’s club, and even though it’s not a huge problem by any means, it is sometimes frustrating to not be able to find a word in the dictionary - and if I’m reading alone, I won’t have a club’s backup. I’m definitely keeping them in mind for later though. Same for Case Closed - I’m sure I’ll enjoy it, but I really want the big blocks of text a novel offers right now.
I’ve looked at it, and while there must be some mystery involved, it seems to be basically fantasy as you say. At least I think so.
Not a bad idea at all, but on the other hand, I’m sure there are so many Japanese writers for me to discover - and I always prefer to read untranslated if I can. Part of the fun of learning new languages 
I’ve already read Suspect X in English unfortunately. I might give すべてがFになる a try - computer stuff of 25 years ago is not foreign to me, but it would be in Japanese I bet. As for ifの悲劇, I did vote for it, so it was on my radar. I’d better not read it now in case it does better next time, I suppose.
Thanks both @NicoleRauch and @rodan for the book lists. I’ll be sure to go through them. It’s not easy to choose straight from lists like that, but it’s certainly a good starting point.
Not unique, surely? Oh, unique, you said. 



Are these children’s books though? I hadn’t heard of them.

. What level would you say his books is? Passed N3?