Mahou Shoujo Elena(2011)

With the help from a mysterious creature, Elena turned herself into a magical girl to beat Zoid, a tentacle monster to save her sister, Emiru. Since that day, to protect her sister and to keep peace on the Earth, Elena started to fight against the ugly creatures as a magical girl! However, what awaited her is a harsh destiny: immoral days of naughty humiliations. Can Elena exterminate the tentacle monster, or is she driven crazy and lost her reason by the ecstasy?