Out of the many anime horrors I've watched, to be clearly honest Pupa was the worst and I've only watched about seven horror animes.
Pupa is about a brother and a sister who ends up with a virus, the sister ending up having the worst of it and now has to live the life of a monster. Sounds pretty good? Welp. Pupa kinda screwed itself over by not really being scary.
One reason being; it tried to be dark but was more like it was just...dark. A lot of the time the coloration of the Anime just seemed gloomy with it's deep colors and it didn't really bring out the chills (for me a least).
The next reason, it went by so quickly. Yes, it is a four minute per episode anime, but you still needed to feel some kind of chill or some kind of fear within each episode. Pupa made it more in a funny way when a character got cut up, or someone got hurt in some way. I spent more time laughing than enough time cringing at the graphic attacks that were going on.
But, I do say there is something about this anime that will make you want to keep watching it, I can't put my finger on it, but the characters can some-what charming in an odd way, it just gonna make you want to watch it. I say, watch it and laugh, don't try and find a generic story.