A series of student suicides occurred at Kitafu High School. One hanged himself in the school bathroom, and two jumped from the school building. They left behind suicide notes with the same words: "I was too loud in the classroom. I need to be tuned." To Tomohiro Kakiuchi, the deaths of the three were undoubtedly suicides—or so he thought. Until he heard what Mizuki Shirase said. "None of them committed suicide. He killed them all." The worst incident occurred in the best class. A lonely mystery begins.