Series in one sentence:
Japan forgets how normal human beings look like.
Series in more sentences:
A boy gets invited over to an exclusive school, but ends up locked inside with a handful of other students. They're told by a mysterious Teddy bear demon they need to kill another student unnoticed if they want to leave, but not without attending a trial first, where they have to point out the murderer. They have to choose correctly, or else consequences.
It sounds like Saw with a hint of Ace Attorney, but it disappoints. It's already hard to take this anime seriously with all the ridiculous character designs it offers. The most normal-looking character is the main one. It took me a while to figure out the large man in the skirt, who was a girl, and the girl who's actually a boy, because Japan.
The lame conclusion of the series is what did it, though. I'm still not sure what the big reveal was exactly, but that's probably because I was too bored to care at that point. Things had turned less serious and thrilling by the time it neared the end.
It had the formula to do something exciting and great, but blew it by inserting this otherworldly nonsense.