I'd actually be fine with the ending not really answering whether the stalker was a human or a demon, but the thing that bugged me was how other characters were acting when considering what has apparently happened to the main character. Seeing the girl he had a crush on just casually walk about doesn't sit right, and I also wasn't quite convinced with how the main's friend was acting. For being what seems to be three days to a week later, the friend seemed to be acting like the whole situation was completely behind him and finished. I mean, he road on his bike doing some investigation to find out the stalker's identity, only to drop the ball once the stalker finally gets to his friend.
I was never scared during the story (which I'm usually not for horrors), but for the stalker being so restrained to human actions (if she was a demon) and for being so persistent in the story, I was impressed with how she felt kinda thrilling by the end - not exactly in her looks but more to her present danger. Good, short manga.
