On the verge of her college entrance exams, Azusa had to give up her family vacation to attend summer classes and ended up staying home alone. Worried about her, her parents asked their niece Miki Sunohara to keep her company. That night, a sudden violent thunderstorm hit, causing a power outage. With no air conditioning in the pitch-black room, the humidity grew unbearable. Frightened by the roaring thunder, the two girls clung to each other, gradually drawing closer as they began to sweat. The scent of their sweat would soon drastically change their relationship...