There are lots of questions that are yet to be answered. For example: Why did the parasites come and from where? Why the last serial killer was able to comprehend monsters and humans just within a glance? and why did he want to kill Shinchi or what was his motive?
These questions were UNANSWERED.
Another aspect I found unnecessary was the female lead. It felt like she was included just for the sake of having a female character, without any significant contribution to the plot. Her role didn’t feel essential to the story’s progression. The same goes with Shinchi's dad. He was a very small part but still, at the end of the anime, I felt he needed some spotlight.
Despite these points, I would still recommend this series to others because of its gripping cliffhangers and the intense suspense that kept me on edge after every episode. I especially loved Tamura Reiko’s character—her compelling development and the plot surrounding her was brilliantly crafted. Her growth throughout the story was one of the highlights for me and obviously the parasite "Migi" is also a noticeable creature. I loved how the feelings in her voice didn't change even though she was a bit attached with Shinchi. The most peak point for me was when Shinchi was gradually losing the humanity in himself, almost becoming a cold and steel heart guy.