A sudden silence cut through the chatter of the students.

High school, 2nd-year Class B. Shortly after the World History lesson began, the homeroom teacher, Mr. Kanzaki, had returned to the staff room to get extra handouts.

In that brief, few-minute void...

Don't move.

The classroom door opens. A stranger stands there. In the man's hand is a rifle with a dull metallic glint.

As the frozen gazes of the students converge on him, the man slowly advances toward the teacher's desk. Only the hum of the air conditioner echoed through the unnervingly quiet classroom, signaling the start of the extraordinary.