Morpheus no Kyoushitsu
In Kishimori Naoto's class, many of his classmates see a classroom in their dream. And the one who were eaten by a monster in their dream won't wake up anymore. Together with his cold childhood friend Kuze Ayano they are trying to solve the mystery that lies behind all those dreams. But, Naoto finds out that only in his dreams there is a door. Ayano feels it's not right to open that door but Naoto.
(Source: Crazy Cake)