Sumire had such a strong libido that her boyfriend broke up with her. One day, while searching for something in her younger brother Katsuhiko's room, she found an unused shoulder massage coupon that she had made for him a long time ago. While their parents were away on a trip, Sumire was masturbating to her heart's content when she found Katsuhiko outside his room, masturbating to himself. Sumire remembered the shoulder massage coupon and gave it to him as a gift: a vagina massage coupon, which she hopes will help him use up all his condoms. While their parents were away, the brother and sister indulged in their sexual desires to their heart's content.