One word Disturbing and thrilling.
From the begining to the end you want more, you want to understand why and at the same time you don't want to... because the answer will probably freak you out more than the question.

This manga, make you wonder about your own life, about the society, maybe about a friend who is like one of the characters... because it doesn't matter wich country is, there is always a 'Saya Kota' in all the societies.