Mahiro Oyama, a self-proclaimed home security enthusiast, has become a recluse, immersing himself in erotic visual novels without stepping outside for years. Concerned for her brother's well-being, his brilliant sister, Mihari, crafts a daring strategy to reintegrate him into society. Her initial move involves creating a concoction that transforms Mahiro into a genuine girl, a development that greatly unsettles him. Now trapped in this unforeseen transformation, Mahiro must navigate life as a charming female until a possible reversal presents itself, if at all.