The Badge of the Unattended Guard

Oh Tae-geon discovers a white door behind the broadcast room wall, one that doesn't exist on any map. The moment he grasps the doorknob, the attendance roster of the missing students begins moving his name to the absence column.

Cha Se-rin receives an invitation to a group chat that cannot be opened. Entering restores conversations of vanished students, but the leave button is sent to only one living student.

Eleven minutes after the blackout, a white fire door appears on the 17th floor where no blueprint exists, and Ryu Geon's name is pushed into the blank space of the resident ledger.