The series follows an unnamed protagonist who returns home to live with his father's new wife and her two daughters, his new stepsisters, Yui and Ai. What begins as an awkward family dynamic quickly descends into a vortex of relentless sexual depravity. The protagonist discovers his stepsisters harbor an insatiable and perverse lust for him. Yui, the seemingly sweet older sister, is the first to make a move, sneaking into his room at night to aggressively seduce him. She uses her body to dominate and overwhelm him, forcing him into intense oral and vaginal sex, milking every last drop of his semen. Ai, the younger, tsundere-type sister, initially acts hostile but her repressed desires soon explode. She joins Yui in their nightly assaults, engaging in frenzied threesomes where the protagonist is their shared fuck toy. The sisters' sexual demands are constant and escalating, exploring every taboo. They engage in sister-on-sister incestuous play to arouse him before turning their combined attention to his cock, working together in a symphony of mouths, hands, and wet cunts to drain him completely. The entire series is a non-stop barrage of hardcore incestuous encounters, with the protagonist being relentlessly and graphically used to satisfy the bottomless, slutty cravings of his two stepsisters.