Tiara

A member of the Guardian World's royal family, Tiara is an agent charged with retrieving the Throne of Yord. She believes strongly in her duty and is well-known as one of the most powerful people in her world: she can both summon elemental beings and transform herself into a demon-like creature in battle. Tiara is hot-tempered and can be abraisive, but is more innocent and naïve than she likes to let on. She was Kagetsu's lover once.

(Source: Wikipedia)