Brother × Sister Complex

The virgin elder brother, Okada Naoto, and the younger sister who's unaware of the concept of chastity, Machi. Machi, who often teases her brother who's never been able to get a girlfriend, and also a virgin of 20 years, with offers to fondle her boobs. While the dominant one in the Okada family is Machi, the one that she's obsessed with is...?