Maiko Fujimiya is a second-year high school student whose hobby is admiring girls' butts.She likes to stand at the bottom of the stairway closest to the female-only train and stare upwards. However, she doesn't adore all butts equally; her type is a big, sexy, plump ass. Fortunately, she has noticed a girl with the perfect butt riding on the same train as her. Moreover, she also gets off at the same station as Maiko. Still, Maiko is content with admirng that ass from afar and fantasising about it, but her life is about the change when the girl suddenly approaches her.

Included one-shot: Himitsu no Zettai Ryouiki (秘蜜の絶対領域)