The plot concerns a group of fifteen-year-olds. The story centers on a boy named Tsuyoshi (at least he thinks he's Tsuyoshi) trying to recover his memories and find a way out of Shibuya. But standing in the way is the system set in place to keep Shibuya as is. One entity, known as "Piece" locks on to any of the fifteen year olds when they become 'broken' and kills them. Shortly the "fixed" children are resurrected with new names and new personalities, and everyone forgets the old version. Except Tsuyoshi and Ema, that is. Ema, Tsuyoshi's only ally, is different from the others. She is the only one--until Tsuyoshi appears--who remembers the dead. She also has the ability to "merge" into a battle suit and with that suit is the only one able to kill "Piece".