Well, if there is one manga that deserves to be explored in such detail after the first reading, it is probably this one.
Let's get the obvious parts out of the way. This is an Asano manga and, as such, it offers the common elements of coming-of-age drama, existential anxiety and depression, hard-hitting social and psychological realism and the overall ugly side of human nature.
The unique aspect of this particular work is the amount of supernatural and philosophical elements who play a decisive part throughout the story and which often blur the boundary between reality and imagination.
I found this work really enjoyable on a literary level, especially since I had never read a manga of such depth. Don't get me wrong, I have read many mature and "serious" manga, but this manga had more levels to it than any manga I have previously read.
The downside of this is that, maybe, it can be difficult sometimes to grasp the story during the first reading. I found myself focussing on the obvious parts of the story during the first go and I accepted that there were some elements that I didn't fully understand yet. In this regard, I often thought of a temporary interpretation of what some things could possibly mean. I assume that many readers will find it equally difficult to understand everything in this book right away and this is why I mentioned studying literature in school in the beginning of this review: Having read the book, I actually went on the internet and looked up sites where other readers had discussed and analysed this book in depth, offering both a summary of story in all its complexity, listing all the themes and motives and putting them in their historical, cultural and philosophical context. I had never done this before with any other manga. I simply hadn't felt the need to do so. But, as a result, this detailled interpretation of the book offered a whole nother level of enjoyment and appreciation for this work.
