Youjuu Kyoushitsu
English title: Demon Beast Invasion
Japanese title: 妖獣教室
Type: OVA
Source: Manga
Episodes: 6
Status: Finished Airing
Aired: May 25, 1990 to May 27, 1994
Duration: 45 min per ep
Rating: Rx - Hentai
Studios: Ashi Productions
Licensors: Central Park Media, Critical Mass Video
Genres: Horror, Hentai
Themes: Mythology

Demons take multiple forms, in this case there's one thats the mightest of all and has to be satisfied with the flesh of woman. He searches for his preys in the form of a woman, so they won't be feared. 

(Source: ANN)