Sanako Hase is infamous within her school—she often seeks sexual relationships with men, causing many of her classmates to call her a slut. While running away from a group of girls who accused her of seducing boys, she encounters the student council president, Yuito Takashi. It's love—and lust—at first sight, and so she asks him out! Yuito promptly rejects her, stating that relationships between boys and girls are strictly prohibited according to the school's rules. Nonetheless, all she wishes is to be his friend, and Yuito reluctantly accepts on one condition: that she follows one thousand rules of friendship.

With Yuito's rules as guidance, Sanako slowly comes to learn what it truly means to be a friend, all so that Yuito can love her back... as a friend.