Having worked my way through Real World, I keep coming back to the introduction of Worm's reading habits. The books by Stephen King that he mentions liking are The Running Man, Carrie, and The Long Walk, in addition to Battle Royale. It almost seems too easy - like Kirino is following the High Fidelity adage that "What really matters is what you like, not what you’re like."
All it takes is a surface gloss of the plots of these books, and Worm's personality is laid out: three of the books are about teenagers (and two of those deal with teens being placed in life-or-death situations by adults), and one is about a man trying to get away from the system. One book deals with an oppressive mother, and all four end in death.
Hell, take the fact that The Running Man and The Long Walk are both books Stephen King wrote under the pseudonym Richard Bachman, and you've got another layer to parse: hidden identity, and whether what's presented is in fact the truth, or if it's a front to fool the world.
A reviewer on Amazon (accurately) noted that the various internal monologues are essentially indiscernible from one another. While I agree, the fact is that each of the girls has her role - slut, brain, lesbian, and plain Jane - externally. Internally, they're all the same, and that's significant. The girls all essentially mention the fact that they feel like none of the other girls would understand what they've got inside, and thus maintain the role they've assumed, yet all the while, each girl is having the same issues.