Hinako, raised as a younger sister, is at that perfect age where she radiates youthful innocence—she's experienced masturbation but remains a virgin. One day, her brother catches her without a bra in the living room, triggering his intense sexual desire, which leads him to take her virginity. Enchanted by the taste of Hinako's body, he begins a series of increasingly erotic pranks. The story unfolds with a bittersweet eroticism, intertwining the pure body of a sister and the overwhelming desire of her brother.