From the title itself you can tell this is a seinen (basically means, 'for a mature audience') story. Which already entails a mature narration, serious characters, and a truly messed up scenario that befalls the stories cast. This story revolves around a group of seemingly ordinary people who have one thing in common. Which is that they've all attempted suicide many times in their lives. So many times in fact that Japan no longer wants to support such burdens and abandons them on an island. In which those who've already given up on life must, ironically, fight to survive. A likely comparison would be 'Lord of the Flies' mixed with 'Battle Royale' but with a more mature cast of characters.
The story starts out with the main character, Sei, waking up in a hospital after a failed suicide attempt and is asked to sign a form after stating his wish to die. The next time he wakes up is on an island with a number of other people, all of which are just as confused as he is. They quickly find a large billboard reading something along the lines that the Japanese government has denounced their citizenship and they are, for all intensive purposes, dead and any attempt to come back will be seen as a violation of territorial waters. Japan seems to defend such actions with the simple ideology that these individuals have given up the right to live, and so the government has given up their responsibility to such citizens.
This manga will keep you interested by its two (but not limited to) of its redeeming features. Which is its realism of the situation and its choice in a main character. By realism I mean the story doesn't revolve around a bunch of misfortunate souls who try to rally together for the common good, it is not by any means a Japanese version of Gilligan's Island. As per a seinen series it contains emotionally distraught individuals who are caught in a horrible situation in which some are trying to help, most do nothing, and others intend to harm the collective good.
Sei, the main character, seems to fit in to the category of an unlikely hero. Though he is by no means a hero, or that there's even a hero in this story. Simply put, he seems like every one else around him on the island at the start of the story, both inept and still clinging to the idea that life isn't worth living. But than he slowly grows in to a somewhat confident and competent man, not unlike his counter part Ryou. Who acts as the groups leader early on in the story, and single handedly brings everyone together to try and survive.
A very interesting read for those in to the psychological and seinin genre. A very cool read for those, like myself, who are a bit tired of over the top action mangas, and want a story that makes them empathize with characters and has them wonder what they would do in certain situations presented in this manga.