A beautiful narrative that's beautifully delivered! I can see places where you probably wanted to expand upon the premise, with the grimoires in your bag though the knife was the only thing you really used. The art direction is brilliant, and blends seamlessly between a Dark Fantasy and what I would nearly call a Sci-Fi setting.
The game is super well-done for everything it wants to be - but it comes at a cost of interactivity. As a player, there was just one thing you could do: Go further down. Of course, you don't have to write entire separate plotlines; but I think it's always a nice way to keep players in a very passive game such as this to give them more ways to interact. The little minigame (the aesthetic of which I liked quite a lot) already helped a bit with that, but when you have enough time, it adds some more to the "gamey" feel. It's still a great game, so don't take that advice of mine too seriously :).
The pacing was a bit slow, too. I go down a long time without anything really changing. For a book it would be more than okay, but in a game it's just a bit too much, if you know what I mean. It caught up very well in the end.
This is all very high-level advice. It was an honor to me to be able to play your game, with such great writing, art, feeling of suspense and clever world-building that incorporates "secret" knowledge of our world that the viewpoint character doesn't have.
Keep up your good work!
EDIT: I forgot to say; the voice-acting was very professional as well.