Morpheus no Kyoushitsu

is a Japanese light novel series written by En Mikami, with illustrations by Yu Shiina. The series began publication on January 10, 2008 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
A mysterious dream "classroom" that many classmates had at a high school attended by an ordinary high school student, Naoto Kishimori. Those who are eaten by monsters in that dream will never wake up.

In order to save his friends who were trapped in a nightmare, Naoto approaches the secret of his dream with his unmanned childhood friend Ayano Kuze. Eventually, Naoto realizes that there is a mysterious door only in his dream "classroom". For some reason, Ayano advises Naoto that "the door should not be opened"

... Can Naoto stop the "nightmare" that has begun to erode the real world? And what is the truth that Ayano knows?