The Drifting Classroom: Perfect Edition Series by Kazuo Umezz

Out of nowhere, an entire school vanishes, leaving nothing but a hole in the ground. While parents mourn and authorities investigate, the students and teachers find themselves not dead but stranded in a terrifying wasteland where they must fight to survive.

A group of students stranded out of time face an internal power coup, a wasteland monster with a voracious appetite and a plague. As tensions mount, the kidsface a harsh truth: they must venture out into the bleak world beyond the school walls in order to survive.