Majuu Senshi Luna Varga
Japanese title: 魔獣戦士ルナ・ヴァルガー
Type: OVA
Episodes: 4
Source: Light novel
Genres: Adventure, Comedy, Fantasy, Ecchi
Studios: AIC, Studio Hakk
Producers: Kadokawa Shoten
Duration: 28 min per ep
Rating: R+ - Mild Nudity

The Dunbas Empire tries to conquer the peaceful land of Rimbell. The three princesses are determined to resist the invaders, expecially the middle one, the tomboyish, sword-wielding Luna. After a magical escapade in the cellars of the castle, she finds herself embedded up to the hips in the head of a huge green reptile, the legendary Varga, and acting as its "brain." Even when in human form she has a reptilian tail. She has to fend off a very persistent giant invader and rescue her sister who has been kidnapped by a pterodactyl.

(Source: AniDB)