NOTE: There are no spoilers in this review.

"There is no despair that can't be overcome by everyday life"

Utsuro no Hako to Zero no Maria (or, in short, “HakoMari”) is a story about what a huge mistake a person can make by turning away from his reality, and if we don't touch philosophy and moral, this is a story about an ordinary Japanese schoolboy, Kazuki Hoshino who was involved in the cycle of various strange and mystical phenomena that were caused by the boxes. And they begin to happen immediately after a new student, Aya Otonashi, is transferred to Kazuki's class.
After that, Aya Otonashi once said to the whole class that she is going to "break" Kazuki Hoshino.
If I will explain the plot further, there can be spoilers which I don't want to touch, but I will immediately go over to the opinion about the characteristics of this creation:

Story/Narrative:
It’s very difficult to talk about the story of HakoMari and not go into the jungle of spoilers, I can only say here that each volume here has its own story about some kind of mystical phenomenon caused by the boxes. What are the boxes? And where they come from? Will be a spoiler if I tell you. I can only say that volumes 3-4 and 5-6 are pairs of "connected" volumes, because the denouement in the first of them (in the third and fifth) doesn't end but continues in the next volume (in the fourth and sixth)...
I can also add that with each volume you are imbued with the concept more and more, reading becomes more and more interesting, more likely due to the fact that after the second volume, the plot in the following volumes becomes only stronger and stronger, as well as the amount of philosophy and moral that the author is very fond of emphasizing because they significantly influence the plot itself, which is not only mystical, but also keeps you in suspense right up to the end of the volume.
The last thing I can say about the plot is that I would advise you to read this work no more than at an average pace, because getting confused in the plot is quite simple here, to be honest - it will be more complicated than in Steins;Gate, but about the quality - the plot is simply indescribable (Dear Eiji Mikage, I can’t even imagine how you sleep at nights after the story you write).

Art/Illustrations:
There is little to explain, I can only say that the illustrations are not perfect - but they couldn't be better. In each volume they feel like they give you a strawberry cake (there is a reference :D) at the top of which there are whipped cream, and you eat them even before you touch the inside... And what about "is it possible to adapt HakoMari?", I think - partly. The first 2 volumes I think it’s possible to adapt, but volumes like the seventh one - almost impossible, and I will be honest, I would be afraid if HakoMari will get an adaptation, because I don't want to see such a creation turned into a trash by some studios... (Tokyo Ghoul adaptation, Studio Deen's Fate/stay night adaptation, and of course - the "unexisting" adaptation of Tsukihime...).
I also want to add that at the beginning of each volume you will see some "thing" in one of the illustrations, which will be somehow related to what is happening in this volume or to the influence of the plot. Either the author who showing you this "thing" at the beginning will just want to say - "remember this little thing."

Characters:
Another of the characteristics that make HakoMari simply an incredible story - is the characters... They have a "+" here not so much in the way that they all have very different personality traits, but rather in how they change and how much their personality is changed compared to their first acquaintance and the moment when their fate, or the fate of someone else, depends on their decision. You will also meet a lot of characters who at first look will not affect the plot, but then you will realize that you were mistaken, for example there I can definitely put Daiya Oomine... And if we talk about "change" - it just cannot be described in words, how Kazuki's personality changed after everything that he went through, and by the end of the story you will see that he is already not the same Kazuki whom you knew at the beginning, and how much his relationship with “Aya” affects the whole narrative and the outcome of the plot, this what makes HakoMari a type of story when the characters influence the plot more than the story itself...
So, about the characters, I’ll say one thing - in this story there are no characters that are shown without a reason, they all somehow affect the plot. There are those that are less, and there are some characters who can literally turn "inside out" all your perception with one "move".

Conclusion + My opinion:
Utsuro no Hako to Zero no Maria was a work that contained not only a story that was brilliant in every sense, but also a work that contained a lot of philosophy topics about real life and moral in general. For example - the ending of this story tells you that we never can turn away from reality no matter how cruel it may be...
If we talk about the ending, I will say that after 2 and a half months of reading (yes, It was very hard to read, so it took me a lot of time), the epilogue and the end of this story, specifically the last lines, caused me to “automatic” tears... I buried my face in a pillow like an ostrich and the whole story flew in my head, and I still can’t understand... Was it because of such a touching and perfect ending? Or because of the fact that there is the end, and I will never find something like this story? Or both the reasons?
Well, if we don’t touch my personal reaction to the end of this story, I will just say that as for me, the ending was perfect and most importantly - it was "right" ...
So, I will say that HakoMari is a work for lovers of Thriller, Mystery, Supernatural and Sci-Fi (if you liked stories like Stens;Gate, Madoka Magica, Death Note and Kara no Kyoukai - then HakoMari is definitely for you!)...
Finally, what about the rate? I think that HakoMari deserves a lot more than "10/10"...

This is my first review so please be kind ^_^