Nishikawa Rion is a young girl deeply curious about fashion and sex. As her bust grows to 100cm and she begins to take on a more mature appearance, her older brother grows jealous of her transformation. Though awkward in expressing himself, he harbors intense feelings for her—so strong that he plots to claim her body as his own. Naturally submissive, Rion has transformed into a gyaru-style girl, yet at heart remains honest and obedient. She follows her brother's commands, enduring repeated torment until she's pushed to climax over and over. This story portrays a clumsy yet intimate sibling relationship where physical exploration becomes their only way of expressing love.