Mahou Shoujo Elena
English name: Magical Girl Elena
Genres: Supernatural, Hentai
Type: OVA, Episodes: 3
Aired: Jul 8, 2011 to Feb 22, 2013
Studio: Studio Fantasia, Rabbit Gate
Source: Visual novel
Rating: Rx - Hentai
Synopsis:
With the help from a mysterious creature, Elena turns herself into a magical girl in order to beat Zoid, a tentacle monster, and save her sister, Emile.

Since then, to protect her sister and to keep peace on Earth, Elena fights against ugly creatures as a magical girl; however, what awaits her is a harsh destiny: immoral days of naughty humiliations, and her battle eventually involves her sister and her dead mother.

Can Elena exterminate the tentacle monster, or will she be driven crazy, losing all sense of reasoning to the ecstasy?

(Source: DLsite, edited)