I've read the novel of this. I say this is my favorite work of the author. Compared to Pancreas and At Night, I think this story could've been executed better but the concept was amazingly brilliant and it was a good read. It was still written well but some things felt like it could've been done more polished.
There's always a pattern of the author just leaving a bunch of things unsaid and for interpretation. It's almost like a signature to their works, but aaaah it is disappointing sometimes. Thought in "At Night, I Become a Monster" that style worked really well. This style always gives a weird feeling after finishing their works, idk it's like so distinct. I feel satisfied but feel like I'm missing something.