@Catlover14: I bet on two possibilities - 1. A girl with psycological/mental problems (and so named as "possessed" but without having real demon possession); 2. It's her sister (or another person) reincarned.
I will really like if this becomes stories of various people that flow around the life of the MC. Sometime they fight together, but for the majority of time simply they live their lifes, will be something really fresh and nice.
Correct me is needed, but I full feel that this is a isekai comedy, not to be taken seriusly. A little mix between Konosuba and Kumo desu ga. I laught at the "gained what-an-idiot title", so it's good for now.
My ideal ending is with the other sensei (that shows sign of being interested in him), and all the other students bonding together as "adopted child" of them.