The Drifting Classroom

The Drifting Classroom manga summary: There is a classroom in the school. No one except me can see it and I accidently entered it one night…After that I have to study in that class with my ghost classmates and ghost teacher who all died in a fire. Why didn’t they go reincarnation but choose to stay in the school? What’s the secret behind the ghost girl that is pregnant? I have to find out truth…