Hina

One of the main female characters. Her secret identity is that she is actually a Guardian Heart, the protector of peace and well-being of Earth. However she must always keep her identity a secret, but it ended in failure just as she arrived at Earth when a high school boy named Kazuya saw the entire thing. She asked him to live together with her, and become "family" so her secret identity would be kept secret. She also has to complete tests given by her superior so that she can stay on Earth. She likes Kazuya and pushes the other girls away when they're getting close to him.

(Source: Wikipedia)