Rito Yūki is a normal high school boy who has a crush on a girl by the name of Haruna Sairenji but he can't confess his feelings to her. One day when he is in his bath-tub, a girl suddenly appears, she goes by the name Lala and is from another planet where she is royalty. Lala has run away because she doesn't want to marry some man that her father has chosen for her and to stay on earth she wants to marry Rito. Lala's father later decides that if Rito is able to protect Lala from her other fiance's they can get married, but if not, he will destroy earth. From that day on Rito's life became quite lively.