If a boy disappears and nobody notices, is he really gone? Hisaki Fujishiro's withdrawal had been almost imperceptible, as hard to gauge as the ebb of a high tide. Even his mother failed to see the signposts, Fujishiro recalls: the elementary-school bullying that broke one of his fingers, the obsession with computer games, the increasing hours spent cloistered in his cluttered bedroom. These were, it seemed, the normal teethings of a preteen in postindustrial Tokyo, just another geeky kid wandering awkwardly through childhood. But gradually Fujishiro retreated completely.
The first tangible danger sign was an obsessive-compulsive disorder that...