Recently having gained weight and unable to fit into her pants, the older sister asks her younger brother for help. However, due to his perverted nature, the brother becomes mischievously aroused and slips his hand into her panties, teasing her with his fingers. This act triggers an escalating series of events, as the brother begins manipulating his innocent and earnest sister. He forces her into bizarrely twisted routines: performing deep throat to slim her face, riding him cowgirl-style to create an hourglass waist, thrusting in missionary position to strengthen her abs, and making her drink cum to achieve smooth skin. A strange dynamic unfolds as the sister's pure nature clashes with her brother's perverse intentions.