Warning:- This manga talks about very dark themes like suicide and there are some very graphic murder scenes, so only read if you're comfortable with that.
This is a very short read, I enjoyed the story but the ending is not that great. So the core theme of this manga is to answer the question what is good and what is evil. If that philosophical question intrest you read the manga. Spoilers ahead.
This manga is the retelling of the story of Adam and Eve, symbolised into modern terms. In this manga there is a character Ai Magase and many people misunderstand that character. Ai is meant to symbolise the evil in the story. She's a symbol not a character and like the story of Adam and Eve where the evil tempted them by giving the apple, here the apple is represented as suicide, a way to escape this modern life.
Although I enjoyed this story, my major criticism will be the answer they concluded that good is to live and evil is to end after all the philosophical discussion they concluded such a basic answer which could be easily challenged by the question why is it good to live? Another major criticism is that the whole story focuses on the character development of Seizaki Zen, who's chasing Magase throughout the story and is also our hero. There were many good characters in this story which never got spotlight.
The best character has to be Magase (maybe I'm getting attracted by evil) it's such a good depiction of evil and nihilist and she's a perfect symbol. The question she asks! Oh my I love her. The manga kept me entertained for 90% of the time, only the ending wasn't satisfactory which I don't mind. So go ahead and read it.