Serial murders start happening in Tozama City, a suburb of Tokyo where a fifth grader named Shinta lives. The killings are so horrible, it's almost like the killer himself isn't human. The keyword that comes up during the investigation is 'M.J'... Is that the name of the killer? After the killings, Shinta's classmate Junpei disappears, but is later found in the sewers. "I can control M.J with my mind," he confesses. Shinta doesn't believe him, but soon enough, tragedies happen just how Junpei predicted they would... In order to uncover the mystery of M.J., Shinta makes a call to Sakaki, an assistant professor from the medical department at T University, who knows M.J's past... This manga contains "Prologue: M.J -Son of Sam-, 'I Saw Him!!'" and other chapters.