Hayou no Tsurugi: Shikkoku no Mashou

Description of anime Hayou no Tsurugi: Shikkoku no Mashou

A resident of the Floating Castle that battle demon beings, the girl Rasutel (Rasu), chosen by the willful lady, the Demon-Breaker sword, is sent on a quest to save a princess kidnapped by a Youki. Her quest is helped by a mysterious Youki called Anshu (but he has basic color that usual Youkis do not have.... hehe!). She is also hampered in her quest by her demon-being oriented younger brother who seeks her golden eyes, the heritage of their father, the Golden Youshu.

(Source: AniDB)