I've never really been into the "play or die situation" types of fiction, so I may have a biased opinion from the start. In all honesty, what really caught my eye in this manga was the artwork. It's really nice, so I wasn't disappointed there. However, as I suspected, the plot didn't exactly do it for me. I read the first eight chapters and had to quit. The "play or die" plotline, as expected, was too contrived for me to believe. Clearly, there are supernatural forces at work here, and apparently, they have their own reasons for acting out this death game fantasy, but realistically, it seems like an awful hassle to set up a whole mass-murdering, highly flashy, police-magnet game for... well, for any reason at all, really. I'm a fairly rational person, so I tend to think that these types of convoluted deathtraps are a waste of time and money, not to mention highly risky on multiple levels. If you want to kill someone, why not just pull out a gun and peg him one? Quick and easy.
What bothered me a lot with regards to the characters was that Kazuki has no problem whatsoever with taking out his classmates so brutally as if he were, as he seems to believe, in a video game. Haruki calls him out on this, but the message doesn't sink in at all, and honestly, I'm fed up with characters whose thinking patterns are so two-dimensional that they can't comprehend such a basic concept as what Haruki is trying to explain. The reveal that
Kazuki and Haruki are both "kings" that need to kill each other
is really typical of manga, and frankly, their relationship isn't so interesting as to make me want to continue reading it just to see how this plays out.
Finally, a minor point but one that really irks me:
After the school blows up and reportedly 800 people die, there is a news report about it. The anchor says something along the lines of, "Our next piece of news is..." before detailing the explosion. I'm sorry, but "our next piece of news?" If a mass death of more than 800 people occurred ANYWHERE, it would be on the front page, the top story, the topic of discussion of EVERY newspaper, news story, and civilian in EVERY country on the face of the Earth. That ISN'T just something to brush off with "our next piece of news" - that is "our only news." I know it's a small detail, but honestly, any moron should know that massacres of 800+ people don't happen every day as a casual occurrence. I'm sorry, but they just don't.
Anyway, I'm giving this series a five for the art and the story (which, though it's cliched and implausible, I'm sure some people would enjoy). The manga seems more shounen than josei. I would have liked to have seen more of the mixing of shounen and shoujo elements that josei (especially Zero-Sum) tends to do quite well. Overall, this manga wasn't really my cup of tea, but if you don't mind fairly unrealistic, suspense-oriented action stories, you'd probably enjoy this.