Re Collection

In order to remember his forgotten dreams, love, and self, Natsume Kanade, a high school teacher suffering from amnesia, is suddenly visited by a strange man with dark-rimmed glasses who claims to be "God".

Natsume Kanade wakes up with a terrible headache from the day before. Wait, what happened yesterday? More importantly, who is he? And who is the the guy with dark-rimmed glasses bossing him around to prepare for school...as a teacher?!

Why does everyone know what happened yesterday!?