The main story is brutal and there is information never provided, but you can guess on it. The thing is, I really liked it, I don't understand why. Be prepared for rape-like scenes and hardcore shit.
Then there's a part, a story that has nothing to do with the main one, that I didn't like. But it's personal. Just... Pure sadism, with no romantic love nor real pleasure. Just dominance and murder. x
Update: The last part, episode 7.5 is called 'paralell world'. I cried my heart out, just to give you a warning. This was very good. It aches my heart. For this being the first work of the mangaka, I can promise they will have a bright future ahead. It was incredible. x
Itou-san (KURAKA Sui)