Forgetful and good-natured Run Momoki has been best friends with Tooru Ichii since childhood. Despite Run being one year older, her carefree attitude and popularity with the boys is a constant headache for the overprotective Tooru. To complicate matters further, when Tooru applies to the same high school as Run, she finds out that their little circle of two has grown into a quartet. Their new acquaintances—Nagisa Tennouji and Yuuko Nishi—are classmates of Run and, in Tooru's eyes, the two must prove they are trustworthy. As a new high school year begins, the girls balance their friendship with the exhilarating opportunities of school life.