Fort Helena is a small town in the Canadian Midwest. A handsome young man named Richard Mackenzie once lived here, registering with a sperm bank and anonymously distributing his sperm widely. According to one theory, he had at least 100 biological children worldwide, many of whom were in the town. Because the residents of this town, which had become "one giant family," could not tell which of Richard's "sons and daughters" were actually his, after a certain generation, romantic relationships with childhood friends or classmates became taboo, and those who attempted such relationships were viewed with the same stigma as sibling marriages in other regions. It was common for young people to seek spouses in big cities, seek partners from other states, or enter into international marriages. School proms became mere "practice," and the faces of students who attended and danced with partners forbidden from romance or marriage became noticeably sallow and lazy. Yuma Nogawa is an international student at a university in Edmonton. His dorm roommate and bad friend Jim introduced him to Abigail, a local student with a hobby of illustration, and they began dating every Saturday.