Tokimeki Mononoke Jogakkou

Arare knows she's a rain fairy - her mother is clearly not entirely human but on her first day of high school she definitely does not expect to enter the Otherworld. Nor does she expect her teacher to have a ridiculously long neck, or her classmates to be a variety of ogres, snow demons, cyclops, ghosts, mist, or the twin-tailed cat, Kiri, and long-tongued girl, Pero, who befriends her. Nor does she expect the veil between the worlds to close behind her, leaving her stranded in this school for girl monsters.