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.

Shiina Kyoko is a high school student in Choshi, Chiba Prefecture, Japan. She organized an event to promote the Choshi Electric Railway Line. The event is a race between the Chosi train and high school student runners. Shiina Kyoko gets impatient as the last high school student runner has yet to be decided. Meanwhile, Mamoru Kumagami is enthusiastic about taking pictures of railroads and trains. He visits the city of Choshi and meets beautiful Kimie. They get closer. Preparation for the event is finished, but an unexpected accident happens.

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.