The protagonist is 30, and helps out his single mother older sister by watching over his niece Ciel on Sundays. At first Ciel was shy, but now she's become familiar, and even clingy with the protag-onist. On this day, she gets flirty together under the kotatsu. "Hey, uncle... Can we do that thing again?" The protagonist then begins to rub Ciel's crotch over her panties. He understands how wrong this is, but day by day his mischief on Ciel grows more intense. He suddenly gets a call from his sister saying that she can't come pick Ciel up due to the blizzard raging outside, and so they'll be spending the rest of the night together.