Haruna Kawai, a busty girl with a dynamite 100cm hips, appears as a monitor subject to observe psychological and physical reactions when unable to use the toilet. She has a rare constitution, urinating only about three times a day, and attempts to endure under conditions where toilet use is prohibited. Once her limit is surpassed, her underwear soaking wet from the massive discharge. Enter Hinena Takahashi, a diaper-obsessed femboy, who decides to put a disposable diaper on her. As big sister Hinena gently wipes and pats her soiled crotch, then feeds Haruna apple juice from a baby bottle, Haruna suddenly wets herself again. Now familiar with the feeling of wearing diapers, Haruna eagerly puts one on Hinena as well. Despite her shock at Hinena's cock, Haruna tenderly wipes it like a caring mother. The increasingly aroused Hinena excites Haruna in return. Wearing matching diapers, the two press their crotches together, rubbing intimately and indulging in erotic sensations. A fancy, sensual documentary featuring an innocent girl with an extraordinary curvy figure and a diaper-loving femboy big sister.