Herds of sand dragons in the desert are stampeding for an unknown reason. A teacher at a school in Emporium possesses a strange power. The Third are investigating a crisis regarding a dimensional distortion.

The expedition group reaches the dimensional distortion, which is called Gravestone.

The dimensional distortion engulfs the group and traps them in an interdimensional threshold. Honoka and Iks both disappeared.

Gravestone tries to kill each separated individual.