Enough is enough!
This mystery follows the rules of Knox’s decalogue! The only exception to this, given that I never specified that a detective even existed, is Knox’s 7th, which will be simply altered to ‘The narrator cannot make any lies in their narration.’ for the sake of there being no misunderstsandings. (And because Lord knows that even if I made them all detectives, you’d find some way to make them unreliable, anyway.)
Knox’s 8th: It is forbidden for the case to be resolved with clues that are not presented! I won’t have this endless leaving and reentering or speculating what Kinzo may or may not have done! You claim that Kinzo left not once, but twice? The first time around, after returning, his precious box would’ve been gone, wouldn’t it have? Wouldn’t he have done something about that? And the second time around - why on Earth would he have left after he presented the situation, clear as day, that he was holing up in his study and did not want anyone entering or not entering?!
Explain, and not through baseless speculation, or perish.
I’m not done, though.
You’ve brought yourself into a corner because I’ve left you with only one mystery to solve in your eyes. That was my mistake.
I shall now rectify it.
Natsuhi did not die as a result of a trap! Which is to say, she did not die as a result of any mechanism or contraption - timed or not - which would’ve allowed the culprit to kill her without being in the room with her.
Yeah, you’re not getting away with this one, either.
Knox’s 10th! It is forbidden for a character to disguise themselves as another without any clues! Even if it was dark, Kanon would’ve immediately realized the person he was talking to wasn’t the same one he’d literally spoken to seconds ago.
Knox’s 8th. Precisely because the design of the work desk was never specified, you lose any sort of proof anyone could’ve hidden in there.
All of the heads Kanon found in the fridge belonged exactly to the people Kanon attributed them to.