Umi Ryuuzaki (龍咲 海)

Umi Ryuuzaki is the Magic Knight of Water. Despite being a beautiful and elegant girl, with a tall model-like figure and long, flowing blue hair, she actually has a short temper, and was initially shown to be the most skeptical of the three. Later on, however, between the three Magic Knights, she took on the mantle of the Big Sister and proved to be very protective of her two best friends, Fuu Hououji and Hikaru Shidou.

(Source: Wikipedia)