In a future Japan, where the birthrate is declining, the "government" analyzes the genetic information of the people and "notifies" them of the best marriage partners under the "Super Fertility Decline Countermeasures Law." Although free love was prohibited once the "government notice" arrived, the matching system on a genetic level was successful, and was called the "red thread of science," and was established as a happy form of marriage. Aoi Nisaka, who is a little more indecisive than other people, is a high school girl who has been waiting for a partner for a long time, waiting for the notification to tell her. On the day before her birthday, her childhood friend Yusho Shiba suddenly confesses to her that he loves her. Aoi is perplexed by the feelings of Yusho, who has always been there for her since she was a small child, when the quiet and mysterious Sosuke Takachiho appears as the recipient of her government notice. Aoi becomes attracted to Sosuke, but...