Schoolgirl Kaiba is a devilish big sister who loves younger boys. When she was in a rut due to too much snacking, her younger brother Mitsuru and his friends Yuyo and Toruya caught her eye...? A few days later, Kaiba meets his brother's classmate, Yuyo, again at the supermarket. She helps him with his many younger siblings and household chores. While helping him, Kaiba stains his clothes and borrows a nursing dress...?