Risaki Matsukaze

Sota Nishino is a good-looking high-school student. He meets Mai, who is his friend Yukihiro Nanase's younger sister. She is also a high-school student and somewhat naïve. Sota Nishino mutters to Yukihiro Nanase, "Your sister is cute." Mai overhears Sota's remark through the thin wall between her room and her brother's.

Kazuto Ishikawa is a first-class architect. He is married to Kiyomi. They have a son, Tadashi, who attends high school and a daughter, Miyabi, who attends middle school. They live together in a refined home, designed by Kazuto. An injury causes Tadashi to quit playing soccer. Since that time, Tadashi often stays out all night without permission. One evening, Tadashi leaves home and does not return. Kazuto and Kiyomi become worried about their son and consider going to the police. News then reveals the murder of Tadashi's classmate. The police suspect that Tadashi might be involved in the murder.

Periods are depicted as pink, heart-shaped sentient beings that harass women on a monthly basis, delivering awful gut punches, but also offering a shoulder to cry on.