[Hashida Mamoru] Facade (Koushuu Yokujou) [YxTL]

Young Hazuki is warned to stay away from the second floor while her older sister Mutsuki crams for exams with the private tutor—but the curious bespectacled girl stumbles into a scene of rope-bound anal torment she was never meant to witness. What starts as horrified discovery pulls her deeper into Sensei's twisted curriculum, her small mouth and tight holes subjected to the same lessons that leave her sister drooling and trembling. By the final page, Hazuki is lifting her skirt and begging to be taught lots too, joining her roped-up sibling in a household where study sessions have become something far more depraved.