Chitose, the youngest daughter of the Usagitsuki family, known for their fertility, is blessed with beauty and spiritual powers, and there is no end to potential marriage talk for her. However, she fell onto a trap set by her older sister Kuon, and is cursed to turn into an old woman. Although Chitose loves children, she had given up her dream on becoming a mother, and spends her days firmly enduring Kuon's harassment. One day, when Chitose turns 18, a mysterious man named Kotaro appears before her and says, "I'll grant your wish."