On a sweltering summer day, 13-year-old Kouta Ochiai comes across a tall and captivating beauty. When their eyes lock, the enigmatic girl snatches Kouta's ice cream and labels him a pervert, prompting him to run away in shame. Soon after, he bumps into his father, who is departing for an urgent business trip, leaving Kouta to live alone for a time. Having overheard the conversation, the girl Kouta met earlier resurfaces and offers to make up for the ice cream by keeping an eye on him. Though hesitant at first, Kouta finally yields to her insistence and lets her stay at his place. The girl introduces herself as Natsuki Hagiwara, a 17-year-old high school student, yet she keeps quiet about her reasons and personal background. Natsuki's arrival instantly liven up Kouta's existence, and as each day grows more risqué and thrilling, he builds self-assurance with her by his side.