This is an ok manga but has some problems. I think its biggest strength is that it has some momentum. The characters have goals and they move towards them. This keeps the story moving forward. However, some of the characters are not very deep and are your cookie cut-out types with many cliched backgrounds.
The art starts off so-so but gets better and more consistent. As a survival story its ok, but could be better. It doesn't quite have the horror level that other stories have. In part this is because its still shounen, and the drama is not quite there. The ecchiness is sometimes just thrown in randomly and detracts from the story line. I mean its a dangerous place, but the girls in this story are constantly taking baths in rivers and streams etc. sometimes by themselves with no weapons. The anatomy of the girls is a bit ridiculous too as most of these characters are supposed to be in junior high (13-15yrs) but they are built like porn stars. Many are ultra-kick butt like the girl who is a nidan (2nd degree black belt) in karate, the delinquent who looks like he's in his 20s and is a genius badass, etc. Yet again many of them are supposed to be in junior high. Meanwhile, the adults come in various assortments such as: dumb, weaker, incompetent, cowardly, murderers or wannabe rapists. We also have some of the female adults that seem to be attracted to these children, which is just bad.
The story also suffers from the common shounen cliches, you know things that we've seen in hundreds of other manga like "must save everybody!" and "must protect my precious friends!" and so on. The male lead is your typical perky hero, who suffers numerous blows to the head which result in no real damage whereas other people in the story become seriously impaired. I guess his head is just harder.
There are some other things that bug me about the story, but I don't want to get too long winded and others have already mentioned some of them. Don't get me wrong the manga is not horrible and can be entertaining, but some of the shounen qualities I think actually drag it down. After reading about 80 chapters I would say it rates about a 7.
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Well I finished it and I have to say that I think it went a bit downhill. The smarter students stand around Akira the main protagonist giving info dumps which was kinda bad. It wasn't necessary to explain every single detail and there just should have been better ways to go about it. We get some lapses in thinking from the mangaka like when our hero leaps down a darkened shaft with no light but he can see the exit and the room he falls into when a few pages before another character was saying how dark it was and they had a flash light. A beastie that was hibernating but should have been dead due to lack of oxygen and other mistakes. More fan service is thrown in, a few plot lines are totally forgotten like the "friend" who was watching them at a distance and we never find out who the masked person is. What happens to those people? Then there is the real big discrepancies like
if they are all clones then how did they end up on the plane? Who put them there? Everyone else on the island had been dead for a long time.
So it doesn't make any sense how they ended up there. This is why it feels like the story is a bit incomplete and the ending a bit rushed. All in all disappointing.