Damn, this was a messed-up manga...
It is 66 (technically 65, but there are two 64s) chapters of pure giant robot battles combined with moral issues.
There is no one main character to this manga. At all.
It starts with fifteen schoolchildren who decide to explore a cave. When they enter the cave, they are contracted into a 'game' of sorts, and told that they cannot back out. The next day, they discover a giant robot that they learn they must pilot and with a fight against another giant robot in order to save their world. Soon after, they discover that the pilot dies after the fight inevitably.
The fifteen characters are supposedly seventh-graders, but they're the most fucked up seventh graders I have ever seen. (I still remember seventh grade...)
But yes, there is not one truly good character in the whole of the entire manga (Rather like the graphic novel Watchmen).
While 66 chapters may seem like a lot, I read this within a few days.
I am going to rate this manga 7 out of 10 because it wasn't that enjoyable, but it was an interesting read, and I have definitely read worse manga. This one is very well-written, but it carries a huge unreal quality to it...